Foot & palm are best channels to replenish body heat in cold countries.
Heating socks (works indoor/outdoor; but can't wash) or heating soles (mainly outdoor; no need to wash) or heating slippers (indoor; no need to wash) are good options.
This heating mechanism shall harvest energy from foot steps (instead of operating with batteries).
Rate of heating need to be automatic depending on the body heat. Colder the body, higher the rate of heat
Handheld heater is one good possibility
This can operated by hand (without batteries).
Manual ON/OFF may not be a problem in this case.
temperature can be controlled automatic or manual setting.