soft tissue injuries are the nastiest… they’re like the game Othello “a moment to learn a lifetime to master” except RSI takes a lifetime to heal.
I would try CC’s suggestions, especially if you have LESS trouble with a pen, tryout a Wacom Intuos Pro tablet. Being a gadget geek extraordinaire, I have one and it is a lifesaver over tedious mouse work. There are tons of youtube videos on setup and use. I had ordered one from Amazon with the intent on returning it if I didn’t like it. Do the same. No worries if you don’t like it.