In my experience the full cheek bit is the best with many youngsters)
I had the same issue earlier this year and tried many different ones. I found that the Dr Bristol bit works the best - they also can't lean on it which helps with many young ones
Try a bit with a little toy inside to encourage the salivation ! something like this for example https://www.orchardequestrian.com/Shires-Loose-Ring-Copper-Lozenge-Snaffle.html
Just get a snaffle and a crop because when he resists you can tap him
A French link snaffle with copper. The happy bit brand has one with a copper link. Make sure your bit is wide enough.