In a previous job, I suffered with arm/shoulder pain, and the occupational health person recommended I try a trackball. I had one of those Logitech ones with the red ball. Whilst it didn't do much to alleviate the problem (a change of posture and having my office chair and desk set up properly sorted that out; the chair was too low, the monitor was too high, and basically all my personal geometry was wrong), I found that I didn't make a good mental connection between the trackball and the pointer. It was an exercise in frustration.
Input devices are fiercely personal. I've also encountered people who use those vertical mice, whereby your hand rests with the edge of the palm on the mouse mat. I can't point at shit with one of those, but everyone I know who chose one absolutely swears by it.
These days, I try not to be sat down for more than an hour or so at a time without getting up, having a stretch, and I've not had a problem for years. Fingers crossed.