Have you tried a standing desk?
I am short, and my arms don't seem long... but I've had shoulder pain and arm pain. Things that have helped:
1. Staying warm! Air conditioning is your enemy.
2. Standing desk. Make sure you have separate levels for monitor and keyboard, so you can put keyboard at exactly right height. Also get a good mat, or your feet and back will hurt.
Long version: https://codewithoutrules.com/2016/11/18/rsi-solution/