Specifically for my hands, I use a Clispeed model zls-a6 Hand Warmer, it fits nicely in the palm of my hand, and it works wonders! The battery lasts for around 5-7 hours at its lowest heat setting (which is still warm for me) and can warm up to 55C (131°F)! You should be able to find one from the link below.
Take Care! https://www.amazon.com/CLISPEED-Portable-Rechargeable-Electric-Handwarmers/dp/B08KDXW469/ref=mp_s_a_1_1?dchild=1&keywords=clispeed+zls-a6&qid=1613785615&sr=8-1 Clispeed Handwarmer