Microheating - Winter

Hi r/Frugal!

TL;DR - I am looking to your input on how to stay warm preferably without using a space heater. Feet and hands are cold - how to microheat?

Background

I am still stuck working at home during the winter, and my apartment has a little sunroom that I setup as a makeshift office. The room is about 1.5m x 3.3m, and it has tile floors. There are two doors that can seal it off, so in theory it is possible to somewhat trap hot air. Indoor temperature in this room ranges from about 14C to 17C (57F to 62F).

I would really like to be able to stay warm without the $$$ and byproducts of running a heater. When up and about then things are perfectly fine, but after sitting for a while my feet and hands get quite cold. I read the microheating article linked to elsewhere, and tried using a heated pet mat. I made a mistake I think and purchased a far infrared one, and it produces almost no heat at all (and did an experiment with seeing if it increases the temperature of water, and it does, just not very fast - about 1C in an hour). Maybe I got a dud.

I've added some old foam on top of the tiles to make it warmer, and that helped. I wear thick socks. The rest of my body is perfectly fine. I wear a down vest. Tried fingerless gloves, but no way I could work all day like that.

Has anybody else figured out how to keep feet/hands warm while stationary? What about one of those ceramic reptile lights under the desk?