I don't see any need for tie-down, martingale, etc. Relaxation and acceptance of tack and aids seems to be the main issue, and the only equipment that should be needed to fix/facilitate that is a good fitting saddle (of any variety/style, as long as it fits both of you) and a well adjusted snaffle bridle.
I think that the dressage camp would be an excellent idea. You can get much better help on site and in person than you can ever get online. Even polocrosse horses can benefit from dressage.