The bigger ball will help for longer sessions I believe.
It always does. No homo.
I've seen folks who made them from threaded rod, pipe and a bike handgrip.
Also no homo.
When I despair, I remember that all through history the ways of truth and love have always won. There have been tyrants, and murderers, and for a time they can seem invincible, but in the end they always fall. Think of it--always.