I agree with black_rose..we use the Snugtime sleep suits and gro bags and long sleeve onesies. No bedding at all except a bottom cot sheet.
I am not sure there is much you can do with rolling over onto the tummy...you could check before you go to bed to see where she is and try and roll her back over, although she may just pefer to sleep on her tummy, alot of babies do.
I know of those things you put into the cots that prevent them from rolling..can't thing of what it is called. It's flat in the middle where you lay them and has anti rolling sides to prevent the rolling. Not sure if they work.