Originally Posted by Charis
If there is one thing I can recommend, it is to have a professional help you find a saddle that fits. Not just a trainer or an instructor, but someone well versed in fitting saddles; the right saddle will make a world of difference in your horse. Think about it this way: it's an essential piece of equipment, like running shoes are to us. If we get a poorly fitted pair of runners, or ones that pinch or rub, or are too big or too small, it not only hurts, but it makes us run and walk funny. The same thing applies to saddles; if they don't fit well, they will hurt the horse. I've seen a mare start to exhibit signs of lameness due to a saddle that was pinching her withers- to the inexperienced eye, it looked like an okay fit. She had a deep muscle bruise and needed a few weeks off to recover before the owner was allowed to use any saddle on her again.
Getting a saddle that truly fits your horse will be well worth the money.
This needs repeating. Please, for the sake of your dear horses back, find a fitter. Online, or in person but someone that walk you through the process of finding the correct configuration for you and your horse.