Since I've had my 12 year old appy (about a year) I've used a one ear headstall. I do not know what kind she was in before we had her, I do know the bit type and we're using the same. She's fairly combative when I put it on her and although we were told she has a sensitive mouth, that's not really the case when you're on her. I do not like being rough with her, but she responds to so little with this headstall.
I've wondered if a nose band might help, and also the possibility of using a headstall with a browband. I like as few contact points on her as possible, mainly for her comfort, but for a horse her size she has kinda big ears and it looks as though the ear slot on this headstall could rub her if we were ever out on a long ride. She's my first horse so we're kinda learning by trial and error.