Hiya catnip

as per what they all said, and in addition, check out the specialized shoes which have a sole shape designed to help your problem.

The manufacturer says this about their sole...
"A raised area in the footbed of the shoe behind the rider's forefoot. Addition of the metatarsal button spreads the metatarsal bones slightly, preventing nerves and blood vessels from being crushed under pedaling load. Result: improved blood flow, less swollen feet at the end of long rides, and reduction of the "hot spots" commonly found with rigid racing shoes lacking supportive insoles and/or small contact-area pedal/cleat designs."

I wear the sonomas and swear by 'em. No, I don't have shares in Specialized.

Good luck