Last winter DS would have the doona pulled up to his waist and since he slept in the crook of my arm I was aware of where he was and where the blankets were. I would alternate sides back then though so he would spend half the night sleeping in between DH and I and the other half of the night sleeping on the outside edge (in one of the anti roll things) with me in the middle and then I would keep him uncovered.
This year things are trickier because he spends the whole night in the middle of the bed and he HATES having the covers over him. He kicks them off even if they are only on his legs but he gets too hot in a sleeping bag or even really warm pj's so for now he sleeps on top of the covers and I cover myself the best I can.