I am currently riding my mare in an original Bob Marshall, and it has fixed all of our saddles fits issues. However, I would really like to get into a treed saddle for myself and still be able to fit her. Unfortunately, I don't have an enormous budget(around 1K give or take) for a custom saddle or even a Double J #10 tree, as I hear that they would fit a horse with her type of conformation. She is broad shouldered, has some withers(last measured at 7 1/2" wide) with a sway in her back, but when you sit on her back she is very flat and round. The problem I was having before with my treed saddles is that they would bridge because of her sway. She has packed on a ton of muscle since I got her as she was on pasture for 8 months before I got her. 

We do have a saddle fitter here where I live, but I spoke with him over the phone and he was telling me the ONLY way I would get a saddle to fit her is to get one that HE made.. and I just did not the fact that he has that I can fix all, be all attitude. 

I recently heard something about a "curved" tree? Is that a thing? Do any of you have horses with similar conformations that work with your horse?

The Double J #10 is really the only saddle that fits him nice, I have tryed many but always went back to the Double J #10. I think Double J came out with a tree that does have more rock to it. But the # 10 fits really nice with a 3/4 5 Star pad. 

The Double J # 10 works for my horse with similar back, but with less pad.

Its called the "rock" of the saddle. and yes I have also been told the Double J #10 is a good tree to try for this type of horse. Look used and you might find something close to your budget. Another one that might work although even used is probably going to be a bit more is a Caldwell rocket. Check their website they have a great explaination of their different trees and the backs they fit. 

Double J does have another Tree thats a #11 and its got more rock and wider in the gullet then the #10, never heard it being called a cruve but if you are talking about the rock in the tree's then these saddles are a good fit. 

I have a mare that is similarly built. She is downhill. I too used (still do for trail riding) a BM but needed to get back to a treed saddle since I don't ride a BM well for barrel racing. You have to find a saddle that fits relatively well then use a bridge pad (I use a Reinsman swayback pad with the BM). I am currently riding in a Billy Cook with a ThinLine pad with the bridging shim. I've used this combo since August and so far so good.

Edited to add: I paid $800 for the Billy Cook. I was tired of spending a fortune for saddles that didn't fit and didn't want to spend more then 1K either.

Thank you all for your replies, I have been doing a lot of browsing around I haven't really found anything under $2000, which I really can't afford at the moment. I have never spent that much on a saddle and I think I'm just dying a little thinking about it lol I too looked into the Caldwell rocket, and the cheapest one I found is $2400. 

Fulltiltfilly, what is a bridging shim? Does it make your horse sore? Do you run in it? 

I will add that my older Original Billy Cook is a great fit most everything ok saddle and those you can pick up for $500-$800 all day long. That really is not a bad place to start. 

Yes I do race in the bridging shim and have trail ridden with it too. She's never come up sore and I've been using this set up for well over a year. I used the booster shim + bridging shim with the BM as well. Again no soreness.

These shims are specific to the Thinline pads.

https://thinlineglobal.com/blog/bridging-saddles-shim-for-saddle-fit-swayback-horse

I have had many a horse built like yours ~  I've had the best luck fitting with a Pro Rider made by Jeremy Bethune, now known as JB Heritage   Lot of rock in the tree and come in 6.5, 7 and 7.5 gullets    The 7 has worked on all but one, and a 7.5 worked on him.

All were race bred, dip behind the withers and ran down hill      Nice riding saddles and wont break the bank   I have ridden a Billy Cook, but had a better seat in the pro rider

I'm going thru that with a horse right now and honestly not even a treeless helped. What made the difference was the pad. I bought a BIO correction pad from classic equine and I have one from Sharon Camarillo on the way to try out. So far i'm loving the bio correction pad. But the one by Sharon is open for the withers which may work even better. Either way no saddle fits him and like you i'm not going to have one specially made. So i would fiddle with your pads as well.