I wouldn't bother with bell boots, they're more to prevent hoof injuries due to over reaching with the back hooves or stepping on them with the other side as far as I understand.
Why is he knocking the poles? Is he just being lazy, are the heights too big, is your plank heavy? If you suspect that he is just being lazy and not picking up his hooves then I definitely wouldn't offer bell boots, that just lessens the impact and in my mind could cause him to be more lazy because hitting your pole doesn't cause any discomfort, therefore why should he have to work harder to jump higher?
I use open fronts when I jump, I only have cheap neoprene inner ones but they do the job just fine while still allowing some air flow in there, otherwise I use tendon boots. Like Lexiie said, Polo wraps don't really support the leg
R.I.P ~ Bubbles - 25yo tb mare - 13.04.2011 ~ 8:30am ~ passed away naturally and peacefully in my arms