I've been doing a little research on western saddles recently, as I'm thinking of buying one, and as most people here trail ride, or hack out, in a western saddle I've ridden in quite a few.
I'm no expert by a long shot, but I'm happy to share what little I've learned.
I would not advise buying a synthetic. I bought an Abetta endurance saddle for my American Paint Horse several years ago. The advantages are they are lightweight and easy to clean - however the trees tend to be narrower, which is a big disadvantage with chunkier horses, like my paint and I suspect your WB. And one of our resident saddle-fitters here says the synthetic tree is far more likely to warp than a wooden one.
Another thing to watch out for is the tendency of western saddles to place one's feet too far forward. I've actually only ridden in one or two that don't do this - a Crates and a National Bridle Shop. I'll look up the links to their websites and post them for you.
I would think for a WB you'd need full Quarter Horse or Gaited Horse bars, but I'm only guessing here as I'm not terribly familiar with the shape of a WB. How long-backed are WB's? Length is another thing to watch out for in a western saddle - too long and it can interfere with the movement of the hips and cause lower back soreness.
Western saddles are trickier to fit than english ones, unfortunately, as an english saddle can be re-flocked but a western cannot - it either fits or you buy a new one.
They are however designed for long periods in the saddle over challenging terrain, and the large tree and heavy skirts help to spread the rider's weight over a larger surface area and are, IMO, more comfortable for the horse, providing the saddle is fitted correctly. They aren't designed for jumping, though - for either horse or human.; )
So my advice would be to contact a saddle-fitter and enlist his/her help.
