I try to avoid sleeping bub in between DH and I because I know he's a deep sleeper and, although I am as well, 'mother's intuition' gives me the ability to not squash poor DD in my sleep. I sleep on my side or on my back, and I rest DD's head on my upper arm (it's always out to the side, bent at the elbow) and if I'm on my back, I bend my forearm down so that it's cradling her against me, if I'm on my side my forearm is up and my other arm cradles her so she doesn't roll away. DD sleeps on her side either snuggled against me, or in a spooning position.
HTH