There are many designs of dressage saddles available, from conventional saddles, to the synthetic and treeless models. It is vital that the dressage saddle fit both the horse and rider, and that the saddle be fitted to horse both mounted and unmounted. A properly fitting saddle is imperative to the horses health and performance, and no orthopedic or gel pad can turn one that is poorly fitting, into one that fits.
If you are unsure how to fit a saddle, or which of the many models are right for you, enlist the help of someone experienced. If you are looking at used dressage saddles, be sure to check the tree, and examine the saddle carefully for signs of excessive wear and tear or breakage. Pay close attention to the billets, watching for dryness and brittleness along with the stretching of billet holes.
There are many new and used dressage saddles available online, and as long as you do your homework, you'll be able to find the saddle that is right for you.