I went through tons of bits - over 20 - trying the find the 'right' one for my TB. It really is more dependent on getting the horse to respond to your seat and legs, more than the bit. Some TBs just don't get it, I think, just my opinion.
I would stick with the softest bit possible. If you have good hands, the kimberwick is fine. A snaffle in hard hands is a lot worse.
Mark Rashid wrote something like, if you want your horse to respond to soft signals, you have to use soft signals. It takes a lot of patience.