I agree with the other gals... you kind of slam on his back at the canter.
There are a few reasons for this, one being the saddle issue-- I'd love to see how you improve in a better saddle. Some saddles are just built with stirrup bars that are set more forward. If I were to ride in your saddle, I'd probably be fine-- I'm 6'2 and my legs could take up the saddle. You'll really benefit from a saddle that not only fits the horse, but fits you! You have to fight so hard to keep your legs in a relatively correct spot that you are unable to properly grip with your thighs, making you tense and very defensive.
Secondly-- you are VERY tense in your lower back. This is why you are hitting the saddle so hard. The lower back, combined with the saddle problem is making it very hard for you to relax and move with your horse!
Try this, where you are sitting right now. Don't move a muscle just yet, but think about your lower back for a minute. Chances are, you are tightening in that area, making you tense in most other parts of your body. Ok, now focus on your lower back and release all tension from it. After doing this, the tension in your entire body can release. Your back, to your legs, do your knees, to your feet. Your back, to your shoulders & chest, to your neck and elbows, to your hands and jaw.
Now, the hard part is to translate this to every day tasks. Try it while you are driving. It is REALLY hard. Doing it while riding is 10x harder, but not only will it help you in all aspects of riding, it will help your horse relax and bring up his back.
Frankly (and with total respect), your horse looks uncomfortable to ride! He is rushing and hollowed out. I guarantee you being tense does not help this! When you learn to relax your horse will not rush to try and evade the pounding into the saddle with every stride, and he'll calm down and like his job a lot more.
It takes lots of practice, and you have to remind yourself constantly to relax. It is hard to do when you are trying to relax your whole body, but when you consider that you really just have to think about your lower back to get that whole body release, it isn't as daunting of a task!
Aim for supple. For yourself, and your horse. You are fighting eachother, and it can change! You can do it!
P.S... I agree that you need to practice two point before you start jumping. What you are doing is hard on his back, as you are acting as dead weight during the jump now and he's pulling you over the jump. Try and move with him, get up in the saddle as he jumps. You will both be more comfortable.
