@rugmankc
I am, what my husband considers, a savant in the art of getting comfortable and sleeping on my back. All the while keeping restrictions in mind and low back pain at a minimum. It is good if you have a firm bed. Might I offer a couple of suggestions....
If you can picture this... One fairly hard pillow placed lengthwise under your op side leg, from the knee down. Then, an even fuller pillow, placed crossway under your good knee and over your op side knee..as close to your crotch as possible. This keeps you from breaking any restrictions in the middle of night, if you have any. I have a 4" wedge at the head of my bed, with two other pillows staggered down. On top of all that, I also have smaller pillows placed under each arm. It looks like I'm in a coffin after all is said and done. The bottom line is this has proven to be very comfortable for me and have no trouble at all getting a good nights sleep on my back....which I was not used to. While this may not work for you or you may have to do some tweaking to suit your needs, it might be worth a try. Good luck.
Oh...and I also have a bed rail placed in the upper third portion of the bed, which has helped tremendously getting in and out of bed.