It’s a tree issue not a gullet issue but thanks!
Once upon a time I had a similar issue–Duett fit the table-backed horse but every model put me in a chair seat. I ended up with an XW Thornhill that checked all the boxes. There are some super-cheap used ones out there. They are decent Argentine copies of European brands; for instance, the Vienna II copies a Passier model. Trees as wide as 36 cm. I’ve had a different model (JC Berlin, a copy of a Steubben) that’s held up well for 20 years.
OMG they have the U shape! But the back panels look long 
@Bloopie - most of the UK brands have a hoop tree (U shape) option and some the XWs are pretty wide. You may want to get another fitter to look at his back. He’s got a decent set of withers in the side view and may not need a true hoop tree.
Yeah, I think as long as the tree points aren’t down in an A shape he should be good. He just needs a little U and a 34 tree.
Maybe see if you can try an Envy saddle. They are made by Custom saddlery on the same trees as their pricy Aviar brand, but they are approx 3500 +/- because they are off the rack, no options. They do have a more U shaped front. That saddle did not work for my witherless wonder, mostly because it had too thick padding in front and back panel. I needed a very close contact panel for a very Wide/ flat, short backed witherless Haflinger. So I had to go up to Aviar. But the Envy might just work nicely for your horse. They rep’s bring the saddle to you to try and the width is adjustable by saddle fitter as the horse changes musculature as they fit up.
I also tried 3-4 Duett models and all of them were VERY uncomfortable for me. At least it was clear enough that I was sure I was making the right decision to not consider them further. I ended up with a Stubben with an upswept panel and am very happy with it.
I just saw one for sale for $1400. 17.5.
I was sooo excited. I literally just texted my fitter and she said no, the tree size isn’t right and she doesn’t recommend even trying it since we know the 34 fits.
Shoot. 
I have years of fitting Arab backs, and still ride a half Arab. Correct dressage work can really change them, so the concept of good enough, and cheap enough, to keep us going might be a direction. Some things that worked for mine were Fairfax and Thorowgood cob saddles for my mare, Thornhill Danube for my long sloping shoulder gelding. The price point dialogue with one’s self has to be cheap enough to be less than you’d lose on brand new saddle resale. My mare, for example, dried out and popped a wither at 11 years old. Prior to that, we sure struggled. My gelding always had a wither, but his shoulders were always pinched. The Danube was acceptable for us and not great. Non slip pads and cushioned pads became important, too.
Don’t get too would up over a supposed tree size/width. What’s called a “34” on one saddle will be a “36” on another. It doesn’t seem to be standard from one saddle to another.
Have you looked at used Prestige saddles? Well made and comfortable.
Or used Passiers. I had several over the years and they seem to fit a variety of horses well.
