Right-hand wireless trackball. (Recommend a mouse for your left-hand also, good to have variety)
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Using a stationary mouse will keep wrist and arm movement down. The trackball being operated by the thumb makes for great comfort (do not recommend finger based track balls).
A trackball doesn't require a large flat surface, though next to the keyboard still tends to be most comfortable.
With 18 months of wireless power, it can be used in a variety of manners not handicapped by a wire.
Con Low build quality
The shell is very cheap, thin plastic and the button sensors are either far too easy to trigger (left/right click) or ridiculously hard (back/forward, middle button/wheel).
Con Really awkward with the left hand.
Doesn't really go both ways