The Logitech Marble is not thumb-controlled, which is probably what OP is looking for. I use the Logitech, and it is amazing. The only downside is that I haven

The Logitech Marble is not thumb-controlled, which is probably what OP is looking for. I use the Logitech, and it is amazing. The only downside is that I haven't figured out how to separate "ball scrolling" from the scroll wheel under Linux. Ball scrolling and wheel scrolling are interpreted as the same key input, meaning if you set wheel sideways to anything else than "scroll sideways" if you want to use a "button+ball" scroll as well.