Unless my right hand (mouse) is very close to my left one, I get RSI.
I started using keyboards without a numpad first, then without the nav cluster. Nowadays I choose keyboard which are taller but narrower, so that I can get the most functionality but without needing to force my right arm too far away: https://tex.com.tw/products/shinobi?variant=16969883648090
It gives my right hand a much better position, it's quick to switch between mouse and keyboard, and it gives my elbows room to rest on the table.
The only downside is that it requires a slightly deeper desk than having the mouse next to the keyboard, but you probably want space on the desk for your arms anyway.
I would also highly recommend getting a trackball, personally I'm a programmer and have to rely on my hands despite having RSI and CTS.
The Scuplt was about halfway to a vertical mouse; the MX Vertical is like, all the way there. It was disorienting at first, but I stuck it out for the first weird day or two and I can't say I've ever been happier with a mouse.