For me the only thing that works is having my legs raised. I actually use two of these Elevating Leg Support and sleep without pain. For side sleeping the softer the mattress the better but i generally prefer to sleep on my back. Try to keep you back elevated slightly if you have any sort of acid reflex. Sweet dreams.
I have similar issues where it's very hard to fall asleep unless I'm on my side. I have pillow I like but they don't sell it any more and it's still not perfect.
When my PT does dry needling on my legs I lay on a flat table and he put puts a bolster under my legs below the knee and suddenly I'm incredibly comfortable on my back, I din'tveven think about thevpillow, and I just want to take a nap.
The bolster looks like this one:
https://www.amazon.com/InteVision-Pillow-Thread-Egyptian-Cotton/dp/B0165VKNNQ
I'm thinking about getting one, just a thought.