[nicwest]

Have you tried the trackballs formerly known as "Clearly Superior" now "Xtrac" apparently[1]. I like the physical scroll wheel and dedicated middle mouse button, the internals are mechanical not optical (I have had problems with kensingtons in this regard), and there are some fairly alluring foot peddle expansion ports on the back that I've not played with yet.

if you do go down this route, I would suggest avoiding a model with an LED in it. while it looks cool for sure the LED is positioned so that shines right in your eyes if you put the device front and center (like in between a split keyboard).

[1]: https://xkeys.com/xkeys/trackballs.html