[adamhorne]

Get a vertical mouse. Now. I used to get wrist pain and tennis elbow (lateral epicondylitis) and it was the difference between working, or not. I highly recommend anything from Evoluent.

And use the pomodoro technique where you can (20 mins on, 5 mins off).

[DeltaWhy]

I can recommend the Anker vertical mouse as a budget option. I use that at home and a large trackball (Kensington Expert Mouse) at work, with a block of foam under one side so it sits at an angle. I found a small trackball to be more painful than a normal mouse, but the large one is an improvement and I didn't have any trouble adjusting to it. But YMMV.