I've had flat and flexible feet for as long as I remember. Whenever I ran I'd always get shin splints and I tried the expensive shoe route where I'd get fitted for the best shoe for my foot type and all that jazz for a sneaker that was $130 and then have to buy a new shoe every 300 miles since I was on the heavier side too. If it wasn't for the military I would have given running long ago as my body just isn't built for it.
Anyway a few years ago I started going the opposite way with the Nike Free shoes and now I've worked myself into the Vibram Five Fingers. I think it has made a big difference in the fact that now I do have somewhat of an arch where before I didn't I'm really conscious of how I walk when I'm barefoot of wearing my Vibram's.
This was a good article- the article is at the link below:
Some things to keep in mind:
-If you are currently overweight dropping some pounds will help
-Do the exercises in the article above as well as other feet exercises
For walking about/running shoes I typically go with one of the Nike Free shoes, I'd recommend trying before buying as they tend to run a little smaller than your regular sneaker size. I personally don't like the Nike Free Everyday shoe but that's because I like the 5.0's more.
For lifting unless I have Oly session I'm wearing my Vibram Five Fingers, for Oly sessions I wear my Oly shoes.
Work shoes...not much you can do here other than find something comfortable.
Boots, I have hard insoles in all my military boots.