Photos would indeed be a help in making more accurate and detailed recommendations. A good conformation photo (examples at http://pantherrunsaddlery.com/?page_id=494) can tell us a lot about your horse’s fitting needs, though we can’t make recommendations regarding tree width/type without seeing a template (instructions on taking a template at http://pantherrunsaddlery.com/?page_id=434 if you’re interested).
As you know, your youngster will go through a lot of changes before hitting maturity, and even after that, his back will change as he progresses in training, so please don’t believe anyone who tells you “this saddle can be adjusted to fit your horse his entire life” - it just ain’t so. At this point in time, something like a Thorowgood might be worth considering. They offer conformation-specific models (high-wither, cob/broadback and standard) that have fitting features geared toward their “target” fit, and have a changeable gullet and flocked panel. This won’t guarantee the saddle will work for years, but it will give you some flexibility of fit. The T4 is fully synthetic, and retails for about $695, while the T8 is synthetic with leather seat and knee pads, and sells for about $895. Either model will give you good bang for the money; they’re manufactured in the UK in an SMS shop, so the quality and workmanship will beat Wintec or pretty much any other synthetic.
