Although using a Marble Mouse trackball is a lot less stressful for this fibromyalgia-filled body than mice or joystick or other trackballs, trying to have my right arm do all the typing (one-handed) and cursor movements AND mouse clicking became too much. So I tried holding a mouse with my left hand that I only clicked. It had its ball removed. This was better but holding a mouse was too painful after a while, so I fastened the mouse to something so I didn't have to hold it. This was better, but the fibro got worse and the clicking became too painful. So I bought a Switch-Adapted Mouse that has a jack for a left-click microswitch. The mouse is out of sight. It's only used at all to have something to plug our left-click microswitch into. A microswitch takes almost no pressure to trigger, so this is the best solution for hand pain, and I freely recommend it to all hand-injured people or those with fibro or arthritis or whatever. If a finger gets sore, switch to another one.

Left-Click Microswitch Wrapped Up with Tape

Switch-Adapted Mouse Has Jack for Left-Click Microswitch