I completely back everyone that says get the horse THEN the saddle. Getting saddlestruck is probably a typical first time horse owner mistake a lot of us fall into (I was one of them, haha I still own the saddle, it's pretty, well made, and will look great as a corner piece in my living-room, but was WAY too narrow for the breed I was into, and ultimately as a result, too narrow for my horse which is of said breed).
Your goals seem similar to mine. I currently do pleasure trail riding, though want to start gearing up for endurance. I am also currently saddle shopping because the last saddle I had fitted by a reputable saddle maker (though NOT a master fitter), was too... dun dun dun... narrow!
My best advice, when you get a saddle, interview the people you are going to have fit the horse. Get an idea if they have any formal training, or if they seem like they actually know what they are talking about. A lot of tack stores will have people who fit horses, however, they aren't actually master/certified/whathaveyou fitters. They just have an idea. This could be unique to TN, but I've run into this issue twice already with two different reputable tack stores near Nashville, and this is a very expensive mistake.
Also, for a trail saddle, you want something with a very comfortable seat and light weight, that puts you in a well balanced position. That is extremely relative and not a general rule. One type of seat would be perfect for one person, while for another, it'd be a nightmare. Me, personally I like a really deep seat, with a twist, which is hard to find in a trail saddle as most are western style. Again, this isn't set in stone, there are exceptions to the rule, and for trail I've found I like endurance type saddles.
Also along with the seat, if you're going with a western saddle with western fenders, if you're short, or have short legs, keep in mind, the shorter you make your stirrups, the more bulk and rigidity is added to your fenders and you lose motion. You may have to swap your fenders out for a smaller size, or if they're leather, have them professionally altered. I'm short, and this has been my main gripe with western saddles, which is why by default I just prefer english flaps+leathers over western fenders.
Don't be fooled by treeless fits all, that's also another case by case situation, and not a rule for all. But if you ever want to try treeless, make sure it's one of the best brands and get the right size (they come in different sizes), for your horse.
Long story short, make sure you get a saddle that fits your horse FIRST, then make sure it is comfortable for you. haha.