Using a cushined mousepad is a mistake. Your wrist should float when using the mouse, so the sooner you get used to that posture the better. Also, consider an ergonomic mouse
nostr:npub13kehwrmfxxjgxv8znskhtv6x8rm90qpgnvdu9rhle2l2ecm200hs3exu6c maybe, but I think most of the issue came from bad posture (again) from using it from the couch from the small table. Why now? I probably ended up hurting the muscle by exgagerating, and it's gonna take a month or two or heal
I bought a beanbag mousepad for general better posture while using it from the couch
Discussion
I've had a couple of weeks with my ergo trackball now, I'm mostly used to it and my right forearm pain has pretty much vanished. Yeah, it was expensive though.