I don't post here often but read very much, so I'll take any bashing as it comes!
First if you really want a pair of great fitting boots stay away from Deter, he over sizes makes them feel good and out the door you go. Over sized boots and a good pack out make for bunions and heel pain. Then you'll end up over cranking the buckles and loose blood flow.
If you have no arch or very little, have a good foot bed made first. This will post you neutral, also the correct arch support will shorten your foot and reduce the width in the forefoot, producing an accurate brannock measurement. Dont try to many boots pick three, too many an you wont be able to tell whats really close to your liking. A tight fit and hot spots are pretty typical, a good fitter will determine how to correct: grind, punch, new liners... If you need alot of boot tuning the best boot to get is one made for tuning: Dalbello, Daleboot, lange, technica. Full tilts are great but the plastic is to thin to over manipulate and the heel/toe pieces are hollow on some older models so you are limited for sole grinding adjustments. Flex is secondary the better fit you'll be able flex a stiffer boot because you'll have better leverage. Flex can be determined by your style, aggressiveness, & skill level as a skier. I would also suggest throwing away any stock liner for an intuition or equal, they correct many simple foot ailments. If the fit on any boot is proper (width and length), pain may still occur but this is normal take them back to the fitter for tweaking. The weather and temp have alot to do with boot pain as well, my feet tend to stay less swollen during the cold months and swell causing pain in the spring. Simple buckle tweaking can fix. Finally, the perfect boot fit can take up to a season of skiing to generate, dont be impatient. Boots are a tool have to take care of them and learn how to use them.
Some local fitters to see:
Dan at Buckmans KOP
Rich Reiber at Rich Reiber pro snowsports in reading
Wolrd cup ski and cycle in Camp Hill
Vermont pro's - worth the drive
Green Mountain Orthotics - Stratton area
Surefoot - Killington
Boots before skis! Good luck...