Why not bitless? You know stopping power comes from training and not whatever you have on his face. If he isn't trained properly it doesn't matter what he has in is mouth (or not), he's not going to listen to you. I tried for years to get my horse to accept the bit. No go. Her mouth just isn't built to comfortably carry a bit. So we went bitless. We didn't have any control issues, and she can be, well... Arab. I had trained her to respond to the aides.

Anywho, rant about the whole "but I won't have any control without a bit" thing over. Have you tried different types of bits? How about a mullen mouth or a french link snaffle? He may like a lot of play in a bit (french link) or it may make him uncomfortable and he wants stability (mullen mouth). There are different shapes of snaffles out there, one probably fits his mouth better than the others. As for exercises, it's very important that YOU are light with your hands and aren't unintentionally catching him in the mouth or giving jumbled cues.

He sounds like a highly sensitive, reactive horse from past posts. I am guessing he puts his head in the air and is very tense through the neck and poll. Any exercise you do should focus on relaxing and not rushing forward. To carry the bit properly he's got to carry himself properly. Focus on softening him around a (large) circle where you're asking him to step under himself with his inside hind leg. I used to do this "sponge" thing with the inside rein in the circle. While asking my horse to engage that inside hind, I moved my inside rein in a very slight, gentle peeling motion. I didn't squeeze my fingers, I moved my wrist like I was peeling a potato. The encouraged my horse to flex slightly laterally and thus drop her head and soften her jaw. She couldn't abide her face being messed with, but she liked this move. Whatever you do, don't nag at him. That will just make him sour on the whole idea. Leave his face alone for the most part and put your effort into getting him to drive from his hindquarters and use himself properly.