I have been coding for so long now that I can't have my keyboard any higher than my lap. I code with it resting directly on my legs. A mouse is right out. Any higher, and my hands turn to clubs.
I love emacs because I can do everything with the keyboard. It is faster and a lot easier on your body long term. My advice, start young. Keep your keyboard directly on your lap and use a ortholinear plank keyboard so your fingers don't have as far to travel. I was skeptical at first, but I will never go back.
Alternate between using the left and right Alt keys. The ergonomist's rule of thumb (no pun intended) is to use both halves of the keyboard. So if pressing Alt-x, use the right Alt button, etc.
I had RSI issues early in my career and this advice alone really helped. Never got the Emacs pinky/thumb. I recently switched to a MacOS and that is giving me thumb issues with the overuse of the Meta button. I now consciously have to force myself to use a different finger when pressing Meta.
Always remember: You have five fingers - no need to keep using the same one/two fingers to press Ctrl or Alt. It will take time getting your brain used to using other fingers for this purpose.
Oh, and yes: Definitely got lots of ergonomic pains due to mouse use. In fact, I changed my career from "regular" engineering to SW engineering partially to avoid having to use a mouse (e.g. CAD SW). And every ergonomist you'll meet will tell you "Memorize keyboard shortcuts and avoid the mouse as much as possible."
As the sibling comment put it, that’s when I look into ergonomics accessories.
My primary mouse is a trackball one, because I have pain in my arm (elbow and shoulder) when I use a regular one on a desk.
I will maybe get a split keyboard in the future. But I did get a mechanical one because of key travel. And I touch type, so I spend less time on the keyboard itself.
People with RSI from constantly reaching for a mouse.