Trackball mice don't need a special mousepad.

You don’t. Trackball mice are stationary — the ball rolls on bearings inside the mouse, not on the pad. The mousepad just gives the base something to sit on, and any flat surface works.

Thumb vs. finger operation doesn’t change that. The ball movement is optical or mechanical inside the casing. A pad won’t make it smoother. If your trackball feels rough, clean the ball and the bearings — that’s the fix, not a different mousepad.

Most people just use their desk. If you want a pad for comfort or to protect the desk, grab any cheap cloth one. It doesn’t matter.

Save your money for something that actually moves.