Not to shill, but these keep your feet warm for less energy than an incandescent lightbulb.
I got these for my house and bought them for my mom, too. And I feel like they would make life a lot more comfortable for people in Europe who want to turn down the thermostat a few degrees.
You do know they make heated footrests right?
https://www.amazon.com/dp/B0013V6PDG/ref=cm_sw_r_cp_apan_glt_i_R5Q98ED71ZTEYN3VN85R
I got a foot warmer off amazon, that helps a ton. https://www.amazon.com/gp/product/B0013V6PDG/ref=ppx\_yo\_dt\_b\_search\_asin\_title?ie=UTF8&psc=1
I have one of these under my desk. https://smile.amazon.com/dp/B0013V6PDG/ref=cm_sw_r_cp_apa_fabc_C19HTVX1NNV26AQN5B4T