The shaft is sort of a D shape - it actually has 2 flat sides, which are adjacent to each other, but my knob has a set screw, so I guess that means my spinner should be fairly compatible with whatever kind of knobs are available, assuming the shaft diameter is correct. I'll have to measure it.
I'd like to know what those "quite a few options" are.

I'm not necessarily looking for something "a bit different" - something more along the lines of "tried and true", "pleasing to the eye", and "good functionally".