I have a bony back, my vertabre stick out. On occasion my back will act up (hurt, get red and tender) from sitting / leaning against the wheelchair back so much. I use a small piece of egg crate cushion behind my back to try and ease the pain. Any other suggestions appreciated. I replaced the aged foam in the back with new memory foam but not sure if that's the best option. Is a dense or a non dense foam best? What thickness should I use? Is there a gel filling that would be better? This has limited my exercise routines, I hope to find a back filling that lets me not have to worry about my back too much. Appreciate the help.