I agree with Alicia, a halter should work fine until you decide what you want to do. If you want to start him in the bit and are already having problems, you might want to have his teeth checked. If they are in good shape, you could try putting a bit/bridle on him without anything attached to the bit and use a halter to steer him. Just let him carry it around for a while until he figures out that it won't hurt him. Letting him graze on a lead with the bit in will help too. When you start using the bit to direct him, remember to use only light pressure and release the instant that he gives. It is almost like teaching a green horse how to give to bit pressure, you just have the added advantage that he is already broke. Although if you decide to stick with a bosal, you should have no problems at all controlling him if that is what he has been ridden in until now.
Also, if he has a problem with putting his tongue over the bits, you might want to try a ported snaffle. That should help a little.