Another personal anecdote: I developed severe pain in my mousing wrist and switched to a trackball. Within a week of switching all pain was gone.

And don't give up after a few days. It took me a month or so to learn how to get the pixel accuracy that I had with the mouse that was a month without pain. Moving your thumb v.s. moving your wrist really helps.

I'm sure this worked for you, but for me a trackball made things much worse. It seemed to be more weird movements in my thumb/hand.

I do notice that if I'm not doing much work (i.e. more browsing with the mouse) things are worse than when I'm working hard (i.e. more Vim)

Which trackball? Logitech Marble Mouse works great for me because it puts my hand in a position that most resembles a hand-shake (relative to other mice and trackballs.) I noticed immediate benefits and thought "Hey trackballs are great!" but then I started using a Mac at work and the scrolling there is not so great so I bought a Kensington Expert Mouse for the fancy scroll ring. Just awful. Wrists flat on the desk, hands bent up toward the ceiling. Worse than a mouse. Not all trackballs are great.