Reason your mouse sticks isn't just that the ball is dirty. If you take out the ball and look inside, you'll see two rollers that the ball presses against that control the cursor movement. You'll see the line of dirt stuck to each of them . Clean the gunge off with a Q-tip and isopropyl alcohol, or meths, clean the ball, re-assemble, and it'll be like new.
If you do go for optical, I'm with Postdog - after several wireless ones, I'm back to a wired mouse, no batteries and a lot fewer problems.