Help propping leg up.

Hello! My lady has been bed/recliner bound since November. She has 2 pressure sores on her right heel and ankle, from a hospital stay in November. They are healing very well and I think she is about to be able to be weight bearing, as of today. We are waiting on that call. She had a King size bed that we had to get rid of and replace with her hospital bed. The king mattress was too heavy for me to move by myself so I cut it up so I could get it out of here. I kept the 5inch foam topper and have used it to make several different “props” for her leg, to float her heel. A lot of trial and error but we finally made one that has been super useful. She was having trouble keeping it on the first ones that I made for just one foot so I got the long rectangle piece and cut out the shape of both of her legs and it keeps her heels about 2” off of the bed. And her foot doesn’t roll off of it. It’s been great! My problem now is that she says the back of her knees hurts. She asked if there was a way that I could put something under her knees and let her feet hang down. I still have a big piece of foam that I can use. I am just at a loss for how to get her knees up and her feet down while her heel still floats. Anyone crafty got any ideas? Thank you.