Problem with the Detente is the horrible resale value. I can’t seem to give one away.
On my Welsh Cob who had a tremendously flat back but a good set of withers. I rode in a Verhan Odyssey, and had the tree slightly widened by Bernardo the owner of Verhan. It fit him like a glove. You can find Odyssey’s used online for way less than your budget. Any chance you’re in Ocala? You could try mine.
Going 2nd DP. I love my saddle and their customer service is amazing!
All of my Welsh Cobs have been built like beer kegs, just that some have had more wither than others. My Morgans have ranged from more slab-sided to full on beer keg. To answer your question, I generally ride in a ‘looser’ girth than most. I can still mount from a mounting block without the saddle shifting but have enough room to go at least one more hole, in some cases 2 holes depending on the horse/saddle. The 3 saddles I currently have for my range of wide bodies are - albion SLK, ancient Roosli pilatus and my semi custom Prestige D1. The Albion and Prestige are both actually MW tree and the Roosli is a wide. I have never found a hoop tree that fits ME and when tried on two of my roundest/widest types in the past, did slide a lot. I am all for getting saddle fitters to assist in these tougher types but at the end of the day it really comes down to trial and error I’m afraid.
Your question though is an interesting one because one of the reasons why I ride with a looser girth (not dangerous/gapping) is that my horses/cobs tend to prefer it and I pay attention to where my saddle is when I ride - is it shifting left, right or staying in the middle/centered. It gives me information about my position and what the horse is doing in terms of stiff side/hollow side. I find it helps my riding in that it keeps me honest about my position and it often alerts me to my horse’s balance quicker and prevents time wasted trying to correct in all the wrong ways what’s going on…
I love Black Country saddles but I rarely see them for sale below $2k. Chunky Monkey(not sure how well known these are) saddles may be something to look into, or possibly an N2. Also, someone mentioned Cardinale…they are very well made and comfortable.