My DS is nearly 11 months and I still can't use a quilt in his cot because he still flips around too much.

I doubt I'll be able to use it until next winter now and even then it'll have to be tucked in well. I think my DD was about 16 months when we moved her into a big bed and she started using a doona (which we tucked into the end of the bed so she didn't tangle up in it).