That your fitter said the issue is where you're sitting on your saddle, is kind of a red flag to me, because it sounds like me.

I need a very T-shaped saddle with a cut-out. More wedge-shaped saddles will force me forward when I pedal, so I'm sitting on the nose and grinding my ladyparts into hamburger meat regardless of whether the rear of the saddle is wide enough for me or not. Before I found a good saddle for me, riding buddies had remarked that I was sitting too far forward on the saddle. It wasn't because of anything related to the cockpit setup, it was the shape of the saddle.

I do very well with a Specialized Lithia (squishier) or Jett (a little firmer) in a more upright seating position. On my road bike, I had to spend a bit more on a SI Turbomatic Gel Flow. For an opposing viewpoint on a domed saddle - I like it because it increases the effective size of the cut-out.