Just one thought, MAG. I have a somewhat delicate right shoulder and it was giving me trouble with a Dreadnaught I played at the time. I switched to a 00 size guitar and that did help a lot. However, now I play with the guitar waist leaning on my left knee (classical position; but without the left leg raised.) and I find that very easy on the shoulder with any size or shape guitar.

I knew a violinist in London many years ago who had arthritis in her fingers. She would wake up with them painful and stiff; but after she started playing the pain went away. The important thing, though, is that she warmed up gradually before she did any real finger-twisters.