Wedge pillow for sleeping?

Hi all—so I'm getting a bilateral mastectomy with reconstruction a week from tomorrow. I don't have a recliner,so I thought I would sleep in bed on my back. But sleeping like that always hurts my lower back so I thought I would get one of those wedge things to elevate my thighs if that makes sense. They have some shaped like a triangle, and others like a trapezoid where your lower legs are raised and horozontal. Not sure which to buy. Did anyone sleep like that and if so, how did it work out?

i found my wedge at Bed, Bath & Beyond, but I've also seen them at Walmart for around $20-25. My wedge really saved the day. I used extra pillows to keep me from rolling over--under my head, under my knees and one under each arm. I also have a small pillow that i propped in my neck, so it was supported when my face would naturally fall to one side or another. I'm a side & stomach sleeper and somehow this tricked me into thinking I was on my side and i was able to go to sleep.

this is what I used. Pricey, but a lifesaver for me!