--- title: "Cot mattresses and safer sleep in the UK | BabyNido" description: "How to choose a UK cot mattress: firm, flat, waterproof, the right size. What The Lullaby Trust wants — and what to skip." url: "https://babynido.co.uk/guides/cot-mattress-safer-sleep-uk" --- - [Home](/) - / [Guides](/guides) - / [Sleep](/sleep) - / Cot mattresses and safer sleep in the UK sleep # Cot mattresses and safer sleep in the UK How to choose a UK cot mattress: firm, flat, waterproof, the right size. What The Lullaby Trust wants — and what to skip. - Safer sleep - Lullaby Trust sourced - UK rooms By [Hannah Cole](/author/hannah-cole) · Published 13 August 2026 · Last updated 13 August 2026 Also browse [Sleep](/sleep)[Newborn](/newborn)[Skip-list](/skip)[All guides](/guides) Desk-researched 2026-08-13. Links marked with * are affiliate links — we may earn a commission at no extra cost to you. Verdicts stay independent: we name the free or official option when it wins. We have not lab-tested products. Verdict The mattress is the sleep product that actually matters: firm, flat, waterproof, snug in the cot with no gaps, and in a clear cot in your room. Skip memory foam “cloud” mattresses, second-hand mattresses you cannot history-check, pillows, toppers and nests. A pretty sheet is optional; a sagging mattress is not a bargain. Not for: Skip this if you need a clinician’s advice for a specific medical sleep system. We summarise public safer-sleep guidance, not prescriptions. On this page - 1. [What kind of mattress should a baby sleep on?](#what-kind-of-mattress-should-a-baby-sleep-on) - 2. [Should you buy a second-hand cot mattress?](#should-you-buy-a-second-hand-cot-mattress) - 3. [Do you need a mattress topper or baby pillow?](#do-you-need-a-mattress-topper-or-baby-pillow) - 4. [How often should you replace a cot mattress?](#how-often-should-you-replace-a-cot-mattress) - 5. [Which cot mattresses are worth comparing in the UK?](#which-cot-mattresses-are-worth-comparing-in-the-uk) - 6. [How snug should a cot mattress be?](#how-snug-should-a-cot-mattress-be) - 7. [Is a waterproof cover enough, or does the mattress have to be waterproof?](#is-a-waterproof-cover-enough-or-does-the-mattress-have-to-be-waterproof) - 8. [Is a travel-cot mattress the same product as a home cot mattress?](#is-a-travel-cot-mattress-the-same-product-as-a-home-cot-mattress) - 9. [Frequently asked questions](#faq) ## What kind of mattress should a baby sleep on? A firm, flat, waterproof mattress that fits the cot or basket so there are no gaps. Soft, sagging or “cloud” surfaces are the opposite of the advice. The Lullaby Trust’s sleep space is a clear cot with that mattress and lightweight bedding only. If you remember one sentence, remember firm, flat, waterproof, in your room. Quote the source, not a brand: “Use a firm, flat, waterproof mattress” and “the safest cot is a clear cot” — The Lullaby Trust safer-sleep overview, last reviewed 1 February 2025, checked 13 August 2026. Room-share for at least six months. Back to sleep. Smoke-free. Source: [ The Lullaby Trust — Safer sleep advice ](https://www.lullabytrust.org.uk/safer-sleep-advice/) (checked 13 Aug 2026). ## Should you buy a second-hand cot mattress? Only if you know its full history, it is clean, firm, unstained, and it still fits with no gaps. A mystery mattress from a marketplace is a skip. Frames travel better second-hand than mattresses. If in doubt, buy a new mattress for an old cot — cheaper than guessing. The Lullaby Trust discusses second-hand products in its baby-product advice. We will not pretend a stained mattress is “fine if you air it”. Waterproof covers help cleaning; they do not unsag a foam core. [ See cot mattresses at John Lewis* ](/go/johnlewis?u=https%3A%2F%2Fwww.johnlewis.com%2Fsearch%3FsearchTerm%3Dcot%2Bmattress&p=inline) ## Do you need a mattress topper or baby pillow? No. Pillows, toppers, nests and wedges are what a clear cot is trying to not be. A waterproof sheet or a fitted sheet is enough. Head-shaping pillows sold for plagiocephaly are a clinical conversation, not a newborn gift. Do not put them in the overnight sleep space because an advert said “safe”. If a product exists to keep the baby in one position, The Lullaby Trust’s list already said no. That includes rolled towels and “anti-roll” cushions. ## How often should you replace a cot mattress? When it sags, smells of damp you cannot explain, or no longer fits with a snug edge. There is no honest universal “every two years” figure we will invent. A second child can reuse a firm, clean, known-history mattress. A stained mystery from a marketplace cannot. If you are unsure, replace the mattress and keep the frame. Waterproof covers make cleaning possible; they do not unsag foam. If the surface hammocks when you press the middle, it is done. Pair with [Moses basket vs next-to-me](/guides/moses-basket-vs-next-to-me) so you do not buy a second sleep product to compensate for a bad mattress. The Lullaby Trust’s product pages are the deeper read on second-hand kit (checked 13 Aug 2026). The NHS Best Start in Life page says the cot mattress should be new (checked 13 Aug 2026). That is the same rule as the car seat: you cannot see a previous sag or a previous crash. A waterproof cover and two fitted sheets are the rest of the bed. Pillows, toppers and “cloud” memory foam are how a clear cot stops being clear. If money is tight, spend it here and take clothes second-hand. ## Which cot mattresses are worth comparing in the UK? Compare size, firmness and a waterproof surface — buy new. Little Green Sheep and generic firm foam listings are common. We have not sag-tested them. Skip memory foam and mystery second-hand. The Lullaby Trust wants firm, flat and snug, not a brand story. [ Compare cot mattresses at John Lewis* ](/go/johnlewis?u=https%3A%2F%2Fwww.johnlewis.com%2Fsearch%3FsearchTerm%3Dcot%2Bmattress&p=inline) Desk-researched 13 Aug 2026. Example UK listings to compare, not a ranked best-of. We have not lab-tested them. Prices move. Affiliate links (*). Awin tracking URLs can replace a hop when you send them. - Cot mattresses · Amazon UK ### Firm flat waterproof cot mattress The product that actually matters in the sleep space. Compare size to your cot (no gaps), firmness, and a waterproof surface. Buy new. Skip if: The listing is memory foam, pillow-top, or a second-hand mystery. [ Compare cot mattresses on Amazon UK* ](https://www.amazon.co.uk/s?k=firm+waterproof+cot+mattress&tag=clevermum0c-21) [Read the buying guide](/guides/cot-mattress-safer-sleep-uk) - Cot mattresses · Amazon UK ### The Little Green Sheep cot mattress A frequently compared natural-fibre UK listing. Still apply the same test: firm, flat, snug, new. Fibre is not a safer-sleep upgrade on its own. Skip if: You needed a Moses-basket size, or you were buying it to justify a quilt. [ Compare Little Green Sheep mattresses on Amazon UK* ](https://www.amazon.co.uk/s?k=Little+Green+Sheep+cot+mattress&tag=clevermum0c-21) [Read the buying guide](/guides/cot-mattress-safer-sleep-uk) ## How snug should a cot mattress be? Snug enough that there are no gaps around the sides the baby could get trapped in. The Lullaby Trust wants a good fit. We will not invent a finger-count their page does not print. If you can see a gap, the mattress is wrong. Buy the size the cot maker states. Measure the inside of the cot, then the mattress, before you keep a sale item. An inherited frame with a random foam slab is how gaps appear. Replace the mattress; keep the frame if it is sound. See [Moses basket vs next-to-me](/guides/moses-basket-vs-next-to-me) so you do not buy a second sleep space to hide a bad fit. ## Is a waterproof cover enough, or does the mattress have to be waterproof? The Lullaby Trust wants a waterproof mattress. A removable waterproof cover helps cleaning; it does not unsag a sponge core. Do not use a pillow-top protector that makes the surface soft. Two fitted sheets are enough rotation. Skip a “cloud” topper sold as comfort. Firm and flat still win after the cover goes on. Worked example: inherited pine cot, mystery foam, a pretty quilted protector. Strip it. If the core hammocks, replace the mattress new. Keep a wipe-clean cover that does not add loft. The NHS Best Start in Life page says the cot mattress should be new (checked 13 Aug 2026). That is the same logic as the car seat. Source: [ NHS Best Start in Life — What to buy for your newborn baby ](https://www.nhs.uk/best-start-in-life/pregnancy/preparing-for-labour-and-birth/what-to-buy-for-your-newborn-baby/) (checked 13 Aug 2026). ## Is a travel-cot mattress the same product as a home cot mattress? No. A travel cot has its own board or foam that must stay firm and flat in that frame, with no extra cushions. Do not drop a home mattress into a travel cot if it creates gaps. Do not add a pillow to soften hotel travel. See travel cots. The home cot still needs its own snug mattress. A second mattress is not a reason to buy a second nest. Clear space, firm surface, in your room at home. Travel is a different frame with the same rules: no extras. If the travel mattress is a hammock, that travel cot is the wrong product. ## Frequently asked questions Should a baby mattress be firm or soft? Firm and flat. Soft, sagging or pillow-top surfaces are not what UK safer-sleep advice describes. Waterproof is the other non-negotiable. Can I use a second-hand cot mattress? Only with a known history, no sag, no stains you cannot explain, and a snug fit. Otherwise buy new. Second-hand cot frames are the easier reuse. ## Read next - [ sleep Moses basket vs next-to-me crib Moses basket, bedside crib or cot: which UK sleep space to buy first, who should skip each, and safer-sleep rules that do not change. ](/guides/moses-basket-vs-next-to-me) - [ sleep Baby sleeping bags UK: TOG and skip Baby sleeping bags and TOG in the UK: which TOG, what to wear underneath, Grobag-style listings to compare, and when a bag is the wrong product. ](/guides/baby-sleeping-bags-tog-uk) - [ planning Newborn essentials UK: what to skip What a UK newborn actually needs — sleep, car seat, nappies, a few babygrows — and the gadgets you can skip. Desk-researched, sourced. ](/guides/newborn-essentials-uk) - [ sleep Cot and cot bed UK: what to skip Cots and cot beds in the UK: one sleep space in your room, mattress rules, furniture sets to skip, and listings to compare — not a nursery theme. ](/guides/cot-bed-uk) - [ sleep Travel cots UK: when you need one Travel cots in the UK: when nights away need one, mattress rules that stay the same, and listings to compare — skip if a Moses basket already moves. ](/guides/travel-cot-uk) - [ sleep Nursery checklist UK UK nursery checklist that starts with a clear cot and a firm mattress. What to skip: bumpers, nests, themes and gadgets. ](/guides/nursery-checklist-uk) - [ sleep White noise machines UK: skip first White noise is optional UK baby kit, not a safer-sleep device. Test a phone first. Buy the mattress before a machine. ](/guides/white-noise-machines-uk) - [ gear Baby monitors UK: who should skip them When a UK baby monitor is useful, when room-sharing makes it optional, and why movement mats are not a SIDS strategy. ](/guides/baby-monitors-uk) - [ gear How to check UK baby product recalls How UK parents check OPSS recalls on GOV.UK: search brand, model and batch, then stop using a match. Not a stale SKU list. ](/guides/uk-baby-product-recalls) [ See compare listings Then hop to the retailer ](#compare-listings)