I saw a diagram in a book from the 70s that I've remembered through all my pregnancies. It showed how to rest so that every part of you was being supported by the bed/floor. I've found it makes a huge difference to try to sleep that way.
So, I sleep on my side, but, like MP, as much on my stomach as possible. My top leg crosses over so it is also on the bed, as does my top arm. I don't use any pillows, except one for my head. And I'm not sure this is the best thing, but I try to limit how much I drink later in the evenings. It means I can make it 6 hours or so without waking up.
My sleep trouble is not me. It's dh! He is a restless sleeper and he keeps me from sleeping deeply. If he sleeps in the other room, I wake up with all sorts of wonderful energy (after I get caught up from being behind, that is). If he sleeps with me...arg...I can hardly see straight the next day. A few days of it, and I ache all over, and can barely function.