Hi Betty,
I was the same in my last trimester of pregnancy. It felt like NO position was comfortable to sleep in. I found that lying on my side and putting a couple of pillows behind me and slightly leaning back on them with a pillow under my belly to support bub was pretty good. It seemed to take the pressure off my back a little bit. Also the one between the knees is great too to stop your pelvis tilting too much.

Hope that helps!