Why the bell boot? That's typically for horses who over-reach and hit the back of their fronts with the front of the hinds. O_O
Since he is actually hitting jumps, I'd say a splint boot. They are more supportive and will make for better padding than a polo. I love my polo wraps, and I don't have a problem doing small jumps in them. My horse tends to over-jump so I never have to worry about her hitting anything, and we don't jump that high.
I don't really know what you mean by polo and splint boots - but I think that's just because I know them by different names.
A lot of showjumpers use open front boots that protect the back part of the leg but leave the front open so the horse can feel the knock so they learn to pick up their legs. If you just pad up his legs he is just going to keep on knocking - its easier for him to jump lazily, and if you want to compete that is not going to help.
What I would do is try to improve your canter and your jump. If you have a round and energetic canter coming up to the obstacle, then the jump has more potential to be better. Also, I would do a fair few grids, even if they are low - getting your horse used to bounces and picking up its feet.
Unless you have a worry of your horse over reaching I wouldn't bother with bell boots. I always use brushing boots (at least) when doing cross country, but depending on the jumping (where, what I am doing, height, type of jumps) I sometimes wear boots and sometimes don't. I went through a bandage stage.