Using a Logitech M570 Trackball here, took a couple of days to get used to it, but really comfortable. It feels weird going back to a mouse & I have much more room on my desk, as it doesn't move.
Good to know, a cheap wacom is good enough. The more expensive can 'feel' more variations in pressure and the angle of your pen on the tablet, but for CAD work that's not needed. These things are more for artwork.
I call this ailment "mousetitis". I agree with others that ergonomics is major contributor to the cause and solution to this problem. I'm guilty of slouching over the course of a day. Tension can also build up without even realizing it.
Of course, I like to blame my shoulder problems on skateboard and BMX bike crashes I had when I was about 14 but these days pushing a mouse around seems to cause more pain. I can't blame it on throwing out my arm playing baseball because I'm left handed.