It'll get better, I swear it will. Riding is a huge learning curve, even if you've ridden before and have been out of the saddle for xamount of years. Hell, I got out of the saddle for about seven months once, came back, had poor muscle, and the girl I originally started lessons with could ride mile-long circles around my bouncing trot all while I was blushing and feeling miserable; but it will get better.
One exercise I've been taught is to stand on your tiptoes, heels in the air, bend your left knee and simultaneously shift your right heel to the ground, rocking your hips to rest your body weight on the floored heel. Then alternate, pushing your left heel to the floor and rising to your tiptoes and bending your right knee, shift your weight to your left heel. Repeat. Start out slow, to get a feel for it, then adjust your speeds as though you were riding a different horse. Standing on your tiptoes will work on building your calf muscles in a similar way to wearing high heels, which can come in handy in riding. The horse's trot is a side-to-side gait, which is what I've been told many students have a hard time learning to handle as they have to move up and down to accommodate the posting trot, but side to side and somewhat against gravity for the sitting trot. This exercise is more about building muscle memory than it is actual muscle, though. It helped me a ton the last time I returned from a hiatus. It might help you. (If standing on your tiptoes is too difficult at first, keep your feet flat on the floor and bend your knee/shift your weight instead. :)
Also, every horse has a different trot. Some are bouncier than others, some smoother, some shorter, some longer. This new horse is, of course, going to be a different ride than your old lesson horse. If you're comfortable with riding him, and not your ability to ride his trot, then I, personally, think you should try to challenge yourself in staying on him and working to improve yourself. Even if it's a lunge line lesson, or five.
In regards to looking for a more secure saddle and being in the wrong place - both disciplines are extremely difficult and challenging as you move through the rungs of riding capabilities and skills you have to build. But they share a lot of principles. Leg yielding, a good seat, being soft on the horse's mouth, balance, and even the posting trot at times, are just some of the things they share. I don't necessarily think you're in the wrong discipline, but I do think you're having a more difficult time with your balance than some. Have you considered asking your instructor to ride in English style in a Western Saddle (if she has one)? Quite a few English barns have a Western saddle for the beginner and younger riders, as it can be a major confidence builder to have something to grab when necessary. If she has one but is unsure as to why you want to use it, you can explain to her that you'd like something more secure to hold onto than the English saddle has to offer; if not, maybe you could try another riding location for a little while and see of it helps.
The path is different for you and me, but the journey begins in the heart.
Last edited by NeryLibra; 10-22-2013 at 12:42 PM.