Get yourself a body pillow. I love mine. I sleep with it everyday. $20 at Walmart.
I lay on my side and do one or two pillows under my head, a pillow under my belly, a pillow against my back, and one between my knees and ankles. The pillow under my belly supports it, while the pillow against my back let's me lay back on my side without actually being on my back. A pillow between my knees and ankles keeps my hips aligned, so I don't wake up with too much pain.
A body pillow is a life saver, since I've bought one I sleep so good. I highly recommend getting one. It supports my arm, my belly, and my leg all at once.
I have two body pillows lol. One for behind me and for in front of me and I lay the one for my back against the wall and put my back on it to support it
I have actually thought about getting a second one for my back. Such a great idea!