change the bit asap.
tom thumbs are pretty harsh, have you tried putting him in just a snaffle bit? Sweet iron works well or copper.
If you want something with shanks you can also do a snaffle with short shanks.
Or you can go to Mylers webpage and check out their information.
with him having a tender mouth, I would honestly try anything, but get him out of that tom thumb for sure.
"Take the time it takes, so that it takes less time."
"Expect a lot, accept a little, reward often."