I got some Volt slippers last year and they are amazing. I lost the charger during the summer, though, and am still searching. In the meantime I bought some socks from Amazon that have little battery packs in them. The tops of the toes stay heated and that's enough for me!
The store where I got the slippers is awesome - https://www.thewarmingstore.com/
edit: add link to socks - there are several brands and varieties though - https://www.amazon.com/GLOBAL-VASION-Rechargeable-Battery-Chronically/dp/B01M679XOM/ref=sr_1_4?ie=UTF8&qid=1542004709&sr=8-4&keywords=battery+heated+socks&dpID=51refIJt4EL&preST=_SY300_QL70_&dpSrc=srch