Saddle help for *narrow? TB/Paint

Hello all, I am new to Horse Forum so please excuse any faux pas I may or may not commit haha :)

I am having the most difficult time fitting my 11 year old TB/Paint. Personally I genuinely believe he is a narrow built horse. Just got a narrow Amerigo CC Pinerolo saddle to try out and it was too wide, and I just didn't like the way I felt in it either. I will post pics of his back tomorrow, ( I just wanted to get this on here asap). Should I just suck it up, call a fitter, and deal with the hefty price tag a semi or fully custom saddle will leave me?

I will post a quick pic that I have of him from last christmas to just give you a general idea of his shape.

Thanks!

Saddle Fitting: Free and easy saddle fit help from the experts

I'm wondering about a #4 tree (medium),

Frankly there aren't that many truly narrow fit horses around nowadays. TBs often get fitted with narrower saddles than they need because of poor conformation behind the shoulder - the tree arch angles should run parallel to the back of the shoulder, not the muscle behind it.

It's worth being aware that quoted tree 'sizes' can vary a lot. For example, in the UK a 3 is a medium and 4 is a wide.