I have a tendency to get a saddle sore only on one side if my saddle isn't just perfect. I tend to get a sore back muscle on that same side. My upper body issues seem to yield to dumbbell work at the gym. I do core specific work both floor and at the gym, and I stretch. That has kept the back working. For a year I did core work using
Core Advantage. That really helped.
I haven't bothered with shims. I probably should have, but I self-corrected OK.