We have just taken the side off our 23 m/o daughter's cot to make it into a bed and want to change the mattress. The one she had is foam and very noisy, which has contributed to her pretty appalling sleep problems. We are desperate for all of us to get a few nights' sleep, so any advice on the best mattress to get her? There seems to be a huge amount of choice(sprung interiors etc) and price. Thanks.