My office admin is using this under her desk. We both have cold feet in the office even with the temperature in the office set at 74. First I tried a panel heater for her and she didn’t find it helped at all. So the next step was this heated foot rest. She loves it and has been using it for a couple of months now.
https://www.amazon.com/Cozy-Products-Toasty-Ergonomic-Heated/dp/B07HHWQSD9