Wired computer mice might seem archaic, but they're incredibly easy to use. This is a slightly more advanced mouse with as many as five buttons.
From Amazon
R-Go Tools HE Break Mouse - Ergonomic mouse - Anti-RSI Software - Medium (Hand Size 165-185mm) - Left Handed - Wired Black, RGOBRHESML
Conrad Electronic
R-GO Tools HE Break (RGOBRHESML) Ergonomic mouse USB Black/silver 5 Buttons 500 dpi, 1500 dpi, 2000 dpi, 3500 dpi Ergonomic
OnBuy
R-Go Tools R-Go HE Break Mouse, Ergonomic mouse, Anti-RSI software, Medium (Hand Size 165-185mm), Left Handed, Wired