The type of breeches etc aren't going to help..your issue here is basic balance. You are simply putting more weight in your right iron than in your left which isn't too uncommon in beginner riders. Lunge lessons without irons would be a good way to help. In essence you need to center yourself in the saddle without putting more weight to one side or the other.
As for posting too high, again, beginning rider issue :). You are posting from your feet, using your feet to push up into the post. For now get used to the motion, the lower rise will follow as you get the rhythm. The actual motion should be more of a sweeping motion back to front using your hips and you use your calf to supply the push vice your foot and the iron. Again, this is all balance related.