I switch between English, Australian & western saddles all the time. In terms of rider position, dressage & WP are pretty close. I use more of a chair seat when riding in a western saddle. For Aussie or English saddles, I prefer a forward seat - and if you want to jump, you ought to switch to a forward seat. If you cannot find a teacher to take lessons from, or if money is tight, at least buy a few books and read them carefully. I recommend these:
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Jumping can greatly increase the risk of head injury. The upward thrust of the horse, the landing, and the position create more risk that riding flat. Folks can debate how much, but I've never seen a study put the increase risk at less than 10-fold! Even if money is tight, a half-dozen lessons might save you a big hospital bill later on. Getting it right from the beginning is also much easier than correcting bad habits later...
The essence of a forward seat is to match your balance with the horse's, so that you do not interfere with his motion as he jumps. The books listed above give a lot of detail. Western is probably easier for a beginner to learn without falling. All styles of riding are hard to do well. The challenge in riding is the horse, not the tack.