At the risk of sounding flippant but go to a good shoe store (A real shoe store. Not a store-that-just-sells-shoes like Target or Wal-Mart) and ask somebody who looks like they might know what they're talking about. And buy TWO pairs and switch them out every other day. It was be easier on your feet and really expend the life of your shoes.
And before you go on your walking vacation be sure and pick up something else you might not have thought about: A walking stick. Believe me, you will thank me. (grin) I know I've seen them now and then in the LLBean catalog and any good outdoor-sporting place/catalog should carry them. If nothing else, do a google.com search. And don't be afraid to spend a little money on these-- either the shoes on the cane. No sense being penny wise and pound foolish.