I used to put B's cot sheet long ways across the mattress so it went right under on both sides and then kept him securely in place. Stopped him rolling over or into the bars.
B was in a sleeping bag too but I just put the sheet over the top of that to keep him in place. He slept like an angel, then as he felt all secure being held in place (might give it a go now and see if I can stop him waking up ).
Nope he still tends to roll.But he now tends to just roll onto his side.If he rolls onto his tummy he will now turn his head to the side.However he will currently only sleep for an hour at a time unless he is in bed in the crook of my arm or can feel me touching his head!! We have a sidecar cot arrangement