Where can I get advice from a professional for finding shoes that fit me?

All my life, I have had enormous trouble finding shoes that were comfortable, or even tolerable to walk in. I've tried lots of shoes (and insoles), including all sorts of shoes made for people with various foot conditions. I've gotten assistance from people who work at shoe stores and spend time helping people find the right--most painless--shoe for their foot condition.

The only shoes I've had that worked, I've found by accident.

The only thing I've learned by experience is that the flatter the soles are, the better. (Any support built into the shoe is always in the wrong place for my foot, making it painful.) Flat part under the sole of the shoe, flat part that faces the ground, flat everything.

So, I'm trying to find someone who's an expert on shoes (e.g. dealer, repair person, etc.) who can advise me on various shoes for sale that might fit my needs. I'm willing to pay. Can anyone suggest where I should look?