You might look into one of those buckwheat pillows - there are a couple marketed specifically for CPAPers. I love mine - you can get the perfect amount of support under your head and neck, then punch a hollow for your mask, and the pillow stays like that until you move it. Because of back issues, I usually have to turn over at least once a night, so I have to readjust, but if you tend to stay in one position it works really well.
Have you tried something else besides a FFM?
I use a nasal pillows mask and I don't have to do anything special to sleep on my side, it's a complete non-issue.
I've been struggling with this too. I've had a couple of back surgeries and cannot sleep on my back if I want to walk the next day. I use 2 body pillows and a pillow under my head. My husband says I prepare my nest before bed. I flip back and forth all night, moving both body pillows under the blankets. And now I've got a mask and a hose to deal with. I tried the Amara and kept waking up choking on condensation from my breath. I've had the best success with the Pica nasal mask, but keeping it in place has been a challenge. I've been achieving 4 to 6 hours with under 2 events per hour, which had my dr dancing when I saw him Monday. I keep waking up with my mask on the floor though, so he suggested we try another mask to find one more comfortable. So I came home with a loaner Dreamwear. It's been awful. 3 nights in a row, I got less than 2 hours per night and woke up in the morning with it on the floor. So last night, I went back to the Pica and had 6 1/2 hours sleep with 1.5 events per hour, but woke up 3x with my mask on the floor, and have been sporting a killer migraine all day :/ My numbers are getting better and better, but I'm still waiting to feel better. At least I'm not getting rainout anymore.