Hi, I just acquired a Fender P bass and have an interesting adjustment I need to make but, I'm not sure how to go about it. The neck is dead straight but, the action is still to high for my liking. The bridge saddles are all the way down basically on the plate. I have another P bass that had the same issue, a local luthier built a shim which just raised the heel of the neck in the neck pocket since the neck angle did not seem to be the issue. My question is, I don't see any commercial shims out there that will do the trick. The ones from Stew Mac change the neck angle. So, it seems to me I'll need to create one. Assuming that's true, what material should I use and how think should it be?