We’re expecting our first baby and need some advice on cot mattresses. Why is the depth important? All we can see online is that mattresses shouldn’t be more than 10cm in depth. We’ve seen a petite sized cot that we like and the recommended mattress is 7.5cm depth. But we’d prefer to buy a mattress from a different brand and it is 8cm in depth. Does it matter? The retailer of the petite cot simply states they recommend their mattress but don’t offer advice on why.