This happened to me also. Put my 4 week baby to sleep whilst on holiday. He had a tendency to sleep to his right snuggled against the moses basket side. As I read previous reviews before using, about the mattress, I placed the cot on the floor and as it was stone, I placed a pillow under the mattress inside the cot. BIG MISTAKE.......PLEASE DO NOT ATTEMPT. On baby's first night inside the cot, I woke to give him his 4am feed to discover his face was lodged in the gap between the mattress and cot side and as I had placed a pillow under the mattress the gap was quite wide/deep. Baby had tipped himself sideways during sleep and ended up face down. Well I had the fright of my life. He was ok and not at all disturbed but I worry what if I hadn't awoke as you hear all these horrible reviews about cot death. Because the sides are mesh I am assuming enough air was passing through. The next night we removed pillow and mattress and placed on top of a quilted duvet.
He is now 4.5 months and using it for up coming holiday. He has now out grown his moses basket but this still fits (just). We are going to place inside the cot provided by the hotel as we are unsure of the standard/quality.