i just wrote a VERY long reply and my internet went down when i posted it!!!! i will tr a shorter version :)
things that need to be considered when fitting a saddle:
1. saddle length - across the back (if your horse is short in the back this is an issue)
2. gullet - the gullet is adjusted to fit the SHOULDER of the horse not the witer. my high withered long backed thoroughbred is in a wide, he's very broad across the shoulders
3. balance - the seat must be centred and balanced - if the saddle is to high at the front, the saddle will tip the rider back and too low in front will tip the rider forward.
4. clearance - the saddle needs to have clearence between the pommel and wither, 3 fingers in my opinion is excessive when mounted, the important thing is the balance.
i once had a show down with gear checkers with my jumping saddle because they were saying it needed to be higher in front. i have it professionally fitted, i have 2 finger clearance mounted and my saddle was balanced. once i did a hard work out and they saw the even sweat marks they never questioned the saddle fit on that saddle.
if you want to check to see if a saddle really fits your horse people, do a hard work out and mae your horse sweat (use a clean saddle pad) and when your done, the saddle pad and the horse should be even sweat marks shaped like your saddle. if your horse has dry bits, then it doesn't fit.
i found this website that might help :) Does Your Dressage Saddle Fit?
also, if your not going to try jumping, then a dressage saddle is the way to go, if you want to try jumping tenan all purpose saddle is the way to g.
i suggest wintec, they can be fitted and they have a changable gullet. they are good value for money, i have one that i was given brand new 6 years ago. be carefull of the el cheapos, they might not be able to be fitted and some are really unbalanced.
good luck and welcome to english riding....if you really want to get a thrill, try eventing :)