Dear Jean,
I can empathise with you in regards to the pain in all areas, but I don't have failing eyesight. Physically I live with an auto immune disorder which puts me in pain levels that by what my Dr says are levels that require narcotics, but I refuse them.
Like you, I have searched and searched for comfortable ways to create art and can tell you that there is none.
One thing I do is use a lot of memory foam in my computer chair and when I paint traditionally, I do hours and hours of it to the point of being near collapse, but my husband puts ice all over me for 24-48 hours after. As terrible as it sounds, I cope this way. Ice is certainly my friend, and sometimes alternated with heat, but not often.
All I can do is offer these ideas and wish things were better for you. I'm so sorry for your suffering.