I found the Aeron great for sitting at a desk for 8 or even 10 hours… with good posture. Slouch, and the Aeron will punish you for it.
The Humanscale Freedom was the first chair that I found was good for sitting in with my feet on the desk, keyboard in my lap. (The headrest support didn’t last, though, it keeps sliding down…)
However, both of these are have been retired to home desk-work chairs. My professional seating is a low, poofy, leather armchair - large (not merely wide) screen thinkpad, no desk at all, just a nearby filing cabinet. Wonderful setup, the matching sofa works well for drop-in collaboration, and it’s lasted several years.
(As for RSI: stop using the mouse 