Try riding without a bit, try riding in a mechanical hackamore.
maybe just a plain snaffle, or a dr bristol
Loose ring rubber snaffle or bitless!
Take away the bit! Horses become more comfortable and happy without metal in their mouths
A rubber snaffle is great! If your horse doesn't like the nutcracker action, you could try a rubber French link. But if he really doesn't like any pulling in his mouth, you could try a hackamore
A simple loose ring snaffle or a rubber snaffle
Leather bits. But still, the rider should mind his hands first.
My horse is very sensitive on her mouth so I've been using a rubber snaffle bit and it makes all the difference for me. Hope this helps!
A nice gentle bit would be an eggbutt snaffle, a rubber D bit or just a simple snaffle. For horses with super sensitive mouths , it's sometimes nice to ride them in rubber coated bits.