debs-
If you cannot find a suitable combination of fins with small foot pockets, and suitable dive boots or shoes, bear in mind that you can make custom inserts for the foot pockets in any fins. There are variou silicone and other plastic products designed for making molds, casting on body parts, fitting orthotics, and even used to custom fit earpieces and hearing aids. They are all somewhat hard to find or expensive when you look for materials that can be used on flesh, but "foot skin" isn't the most delicate to start with.
With any of these products, you could mix up a batch inside the foot pocket, then insert your foot firmly, strap it in or have a friend help position it, and wait about 20 minutes for the material to harden up. Remove the foot (did I mention, grease it?) and now you've got a custom foot pocket.
An orthotic or orthotic shoe fitter should be able to work with you if that's more complicated than you want to deal with, but of course they'll be pricey.