Does anyone use a wool / sheepskin cot mattress topper? My one year old seems to sleep better on the bed on top of the duvet but we can't leave him there as he will roll off! We're wondering if it's because it's cosier than his cot mattress which feels very hard and cold. I know advice is to have them directly on the mattress when they're little but as he's older now, will this be safe? Any recommendations for a good mattress topper? The ones I'm looking at seem to be close to £100 which is very expensive! I don't want a small sheepskin either as he's not likely to stay on it so I want something that covers the whole / nearly whole mattress.