Logitech Wireless Trackball M570

Trackball mice are comfortable to use and are widely known for being one of the most comfortable and accurate types of mouse. They provide fingertip control of the mouse pointer allowing you to reduce unnecessary wrist and shoulder movements that can cause discomfort and injury. 

Comfortable ergonomic design
The large ball provides long-lasting support for the hand and precise cursor control
Stable base - The hand stays comfortable all day long with this stay-put design.
One-touch access to common tasks and activities, programmable Forward/Backward buttons for faster internet navigation, and a drag-lock button for more control
Fingertip-based control provides fast, accurate cursor movements
Marble optical technology - smooth tracking on almost any surface, so the user can be productive wherever they work.