Carl,
First, I assume you're using some form of wrist brace. This is good - very likely to be helpful.
Second: use a trackball.
When using any pointer-based activity in the computer, we're doing small-movement tasks. Our fingers are designed for, intended for small-movement tasks. Precision tasks.
A mouse uses our shoulders and arm muscles. The large-movement muscles. Shoulder and arm muscles should be used for big movements. Spears and scythes. Or for more modern stuff, basketballs and lat-pulldown bars.
A pencil, a spoon and a trackball use the small movement muscles.
Adjusting to using a trackball when you've always used a mouse is difficult, I fully understand that. But shifting to a trackball really really helped me. I was pushing through agony to use my mouse. I decided it was worth a try. Now? No wrist problems at all.
I strongly recommend the sort of trackball where you move the ball with your fingers, not your thumb.
The first trackball I used was a Logitech 'Trackman Marble'. It's good enough, but the lack of a middle mouse key makes it only barely useful in the modern era.
The second I used was the Kensington 'Expert Mouse'. I liked it better than the Logitech, but if you can't span an octave on a piano with your hands it's kind of stretchy.
I now use an Elecom Deft. Downside: the default manual is in Japanese and the translator doesn't have the best grasp on English grammar. Upside: that's the worst downside.
If you can span an octave on a piano, try using the Huge variant.
I'm not intending to provide medical advice, this is strictly patient-to-patient talk.
And I'm not intending to promote trackballs as some sort of Trackball Expert or Trackball Guru. The switch to trackballs worked for me. I hope that others with the same problem find this helpful. Specifically (at the moment), Carl.
You are my go-to with all Sims info, Carl. I value you, and I value the invisible-to-me support Pam was. May her spirit live on in memory, and may her good wishes be with you all your life.
Tarrel.