I definitely feel for you... in women's shoes (especially heals) fit is incredibly important. You can be a size or two large in a men's shoe and be "ok"... not comfortable, but not in exquisite pain, either.
I third, fourth, and fifth the comments about Payless shoes. My experience there has been excellent. I bought five pairs the first time I went (I'd budgeted about $120 for shoes, that was my big transition purchase that month). I was left undisturbed with my girlfriend except when we had a question, and no one even looked at me crosseyed when I tried the shoes on myself. It might help that the large sized shoes are all on one row.
The take-away from this is that, while I have a size 12 foot in men's shoes, in women's shoes (at least the ones I tried) I could comfortably fit into some size 13 or even 12 flats, and size 12 heels (possibly because my feet are very narrow and I have an extremely high arch).
You can buy shoes online, but I really recommend going to a store and *finding your comfortable size* first! Take a couple of pairs home, and get used to them, then buy fancier shoes for less online.
Amazon.com has a lovely filter by size option.
Oh, and another tip: Create a new email address and set up a new Amazon account for your new life... that way when you log in to that account on Amazon you'll be offered sales and promotions for the products that are most important for the real you. It's amazing how ads tailored to the real me have a tangible impact on how I feel about myself.