Medium Tech: Get some good Sorrel or Columbia or other winter
boots and stick some of the chemical boot warmers sold at hunting and
ski stores. Heat Treat Toe Warmers for instance: http://www.rei.com/product/405012

You could do like a certain USAF Test Pilot did on a wave sortie and
drop some of these inside you pressure suit (100% O2 environment).
Apparently they get your feet REALLY warm - like burned badly enough
to be laid up for a while. Guess he skipped thermochemistry......