I recently went to a MGW Gripper knob (with my new MGW shifter), that is supposed to be good in hot weather...there are several different inserts available, and a stainless nut/collar or anodized collar. I have the anodized, but the stainless insert and nut weighs a little more, which might help with the shifter vibration you describe. It is 6.25 inches in circumference on my tape.
I had a Hurst T grip years ago that was a good handle as well.
Maybe a local machine shop could make one large enough for your hand if nothing else seems large enough?
Underestimate me, that will be fun.
GREEN WORM RACING--since 1959
These are my opinions...YOU are responsible for YOUR decisions and YOUR outcomes...AND, my not arguing with you does not indicate agreement with your opinion.