I think the fact that you went to several shops and got so many different issues speaks to the fact this is not a fit issue.

If it were, you would have had a) more unanimity, and b) it solved already. Getting comfy on a bike is not rocket science; look at your garden variety cruiser for a primer on the core principles. Also, I believe that if a bike isn't properly sized, you'll know it right away, as you'll feel too stretched out, or about to pitch forward, or too cramped. Anyway, "fit," in cycling parlance, is about optimizing performance, not comfort.

No, I think actual discomfort is more telling of a setup issue, which differs from fit in that alterations do not change factors such as stem length, handlebar height, top tup length or saddle position.

What I suggest you focus on first is your bike setup:

--make sure you're brake levers are angled down sufficiently that your fingers find them easily without having to reach up, especially if, as in smart city riding, you are covering your brakes frequently. Reaching up to get on the levers will put pressure on your wrist and heel of the palm, causing discomfort.

--if you're riding a suspension fork, make sure it's properly sprung so you're not sagging into the travel too much while riding, which can upset the riding position you planned for back when the shock was properly set.

--as mentioned above, vary your grip, esp. with the addition of bar ends.

--ensure your grips aren't rotating on the bar, allowing your hand position to shift.

--get good grips, with tangible padding. Some are very thin.

Finally, I can guarantee switching to a drop bar will resolve your problem...if only because of the change of hand position. I do not necessarily think this is the way to go, however, because you CAN alleviate the problem with less hassle, less cost and without losing the urban advantages of the flatbar, through proper setup.

If all else fails, BTW, it's a fit issue.