I've purchased a new cot mattress for my second baby and it's smaller than the one I used for my first child in the same cot, despite being the manufacturer's recommended product. There's a 40mm gap between the mattress and cot end (and 30mm between mattress and cot side) when it's pushed to one end. This seems compliant with the Australian standard but your website states "Make sure there is no more than a 20mm gap between the mattress, the cot sides and the ends of the cot." Is it safer to use the well-fitting mattress my firstborn had (which was purchased new 3 years ago and used for almost all that time) or use the new mattress that's smaller? I feel like I have to choose between new and clean and too small, or well-fitting but used and perhaps less firm (because it's moulded to another baby's body). Advice would be much appreciated!