In my experience most saddle brands use the same tree for all their models unless they specify differently. Some brands say they have a cob, a draft, and a TB tree for instance. That’s why one brand usually cannot be made to fit all horses.
It is indeed hard to judge anything from photos. I would think a quality consignment shop would work with your tracings. Some actually have instructions to do tracings.
After a while you learn what brands are a good bet for your horse. For instance, I took back tracings for my big Paint to a good travelling consignment shop that specialized in high end French foam jump saddles. It became obvious she was just not going to fit in any of them, so that let me rule out a lot of brands. The seller knew her saddles and obviously was motivated to make a sale, so I tended to believe her. On the other hand, Passier and County fit her well.
You will learn as you go. Getting useful feedback from knowledgeable people is important.
Remember too that the front to back horizontal curve is important but so is the vertical drape. Everyone pays attention to this at the withers but it matters all the way back. Panels can be too steep or too flared for proper contact all along the back.