I know a bit about this, as I wear a women's 6 1/2EEEE. Seriously not fun. As a kid, I had to have custom made shoes. As an adult, I have my cowboy boots custom made and the remainder of my shoes are Crocs and Propet. I can't wear most styles of Crocs, as even they are too narrow. The standard beach works, as does the Scoot. In addition, I have found that the only flip flop that I have ever found wide enough is also by Crocs. The only flip flop that works is the Crocband Flip ordered in a size larger than I usually wear. I am always excited to order the new color every spring! For the record, Crocs is having a sale from now to 3/23.
For "Fancier" sandals and shoes, I order Propet shoes. They are well made, reasonably stylish and have a 1,000 mile walking guarantee (for what it's worth).