I bought my mom a used hospital bed when she had COPD and couldn't sleep flat but it was an older one. She did sleep well in it.
When hubby had his open heart surgery, he couldn't lay flat. Sad, too, because I had spent $1000 on a brand new queen size mattress and box spring a couple months before his problem. I saw a "free ad" for a Craftmatic single bed and called. I was #5 in line for it and evidently, no one else took it. He enjoys sleeping on it. The new mattress and box spring is leaning up against the wall.
I sleep on a sofa bed due to the tenderness of my knee and it's very uncomfortable. I use 3 pillows to elevate my head. I have the sofa bed mattress with an egg crate mattress and some kind of puffy mattress pad but neither help. i don't know if the springs or the mattress itself broke, but where my butt is, there's a big indentation and it's really more than uncomfortable. LOL The rest of the bed is "puffy" because of the extras but they flatten out when I lay there. I would love to get an adjustable bed but can't afford one. I saw where the frame alone is $599 in one store.