A cot mattress gets chosen in a hurry more often than almost anything else on a nursery list — usually because it arrives bundled with the cot and nobody thinks to check it separately. That's a mistake. Firmness, breathability and materials matter here in ways that don't apply to adult mattresses at all.
Here's what to actually check.
Step 1. Firm Is a Safety Requirement, Not a Comfort Preference
For babies, a firm mattress isn't the "supportive" option on a comfort spectrum — it's the safe one. A soft surface lets a baby's face sink in, which is a genuine suffocation risk in the first year. Press down on the mattress: it should give slightly and spring straight back, not leave a lasting indent.
Babies don't need sleep zones. Adult mattresses often have different firmness across the shoulders, hips and legs, matched to how one body lies still all night. Children move constantly through the night — turning, rolling, ending up sideways or diagonal — so a single, consistent firmness across the whole mattress is what actually suits them, not a segmented adult-style design.
Step 2. Check What "Breathable" Actually Means
"Breathable" gets used loosely. What it should mean is that air genuinely moves through the mattress core, not just that the cover fabric feels light.
Open-pore foam cores let air circulate through the mattress itself, helping pull moisture away rather than letting it sit against the baby. This matters more for babies than adults because young children aren't yet good at regulating their own body temperature — the mattress is doing some of that work for them.
A honeycomb or channelled core layer is another way manufacturers build in airflow, particularly for smaller cradle and Moses-basket mattresses. Either approach is valid — what to avoid is a solid, sealed foam block with no airflow structure at all.
Step 3. Look for Certifications That Actually Mean Something
"Hypoallergenic" printed on a listing is a marketing claim, not a verified standard, unless it's backed by an actual certification you can check.
Oeko-Tex Standard 100 tests for harmful substances in the finished textile, including the foam and cover — this is the certification to look for on the core material itself. GOTS (Global Organic Textile Standard) applies specifically to organic cotton covers and confirms the fibre was grown and processed to organic standards, not just labelled "organic" with nothing behind it.
Neither certification is essential for safety — plenty of good mattresses aren't certified — but if a listing uses words like "hypoallergenic" or "organic" without naming a standard, treat it as unverified marketing language rather than a fact.
Step 4. The Cover Matters as Much as the Core
A mattress core rarely fails you day to day. The cover is what you deal with constantly — spit-up, leaks, general mess — so check it properly before buying.
Removable and machine-washable is the baseline. Beyond that, check the actual wash temperature: some covers only need 40°C, others are rated for 60°C, which matters if you want a genuine deep clean after illness rather than a quick refresh. A cover rated for the higher temperature gives you that option later even if you don't need it immediately.
A waterproof layer laminated into the top of the cover — not a separate plastic sheet — protects against leaks without trapping heat the way a fully sealed waterproof mattress protector can. Check whether the waterproof side is clearly marked, since laminated covers are sometimes only waterproof on one face.
Step 5. Buying for a Bed That Will Grow
If you're buying a cot or junior bed designed to extend as your child grows, check the mattress situation at the same time — not after.
Some manufacturers sell a matching mattress extension rather than requiring a whole new mattress when the bed frame extends — Chicco does this directly, selling replacement mattresses sized for its own Next2Me Evo & Essential and Next2Me Forever cribs — for example, a cot mattress that extends from 68 × 122cm to the full junior size once the bed itself is extended. This is worth checking specifically, because it changes a "buy a new mattress in two years" cost into a much smaller top-up.
The practical question: does this specific mattress have a matching extension available from the same manufacturer, or will extending the bed mean sourcing a completely different mattress? Check before you buy the bed, not after.
Quick Picks by Budget
Budget: Shnuggle Quilted Moses Mattress — £15.95, fits any standard Moses basket.
Replacement, Air Lite: Shnuggle Air Lite Replacement Mattress — £19.99, breathable hypoallergenic fibre.
Replacement, Next2Me Forever: Chicco Next2Me Forever Replacement Mattress — £74, sized for Chicco's largest bedside crib.
FAQ
Does a cot mattress need to be certified organic to be safe?
No. Certification (Oeko-Tex, GOTS) confirms specific materials and processes, but plenty of safe, well-made mattresses aren't certified. What matters for safety is firmness and fit within the cot — certification is a materials-transparency bonus, not a safety requirement on its own.
How firm should a baby's mattress actually be?
Firm enough that it springs back immediately when pressed and doesn't leave a lasting indent from a hand or elbow. If in doubt, firmer is the safer direction to err in for the first year.
Can I reuse the same mattress across every bed stage?
Only if the manufacturer explicitly sells a matching extension for it. Otherwise, moving from a cot to a junior-sized bed usually means a genuinely different mattress size, not just a longer version of the same one.