You can walk into any major retailer, buy a space heater, and plug it into any outlet in your home. Keep in mind that your gas furnace is turned on/off using a thermostat and temperature setting, so if you reduce the set-point e.g. 1 degree, and then either locate the coldest parts of your home or areas you want to prioritize (e.g. livingrooms/bedrooms), you can then target space heaters into that location to offset the savings from gas.

In terms of deployment heating or cooling, electric heat is the cheapest and easiest. You're just thinking that it must be whole-home or nothing, which isn't the case, you can reduce your whole-home and spot-heat as needed.