Quartz heaters as needed is what i do in places I have no other source...old coal fireplaces are pretty and will burn a little wood too but make sure they draft nice...small fire only...but they are not much for heat...a buckstove will run you out of the home in all but NE South Carolina in winter.
I’m in Nashville metro...probably median winter US wise..going without heat in a bad winter here like two years ago would be rough
If the building and wiring are old, the current required by the heater/air unit may be pushing the limit of what the wiring can handle. Feel the plug/outlet area after it has been on awhile and see how hot it is. Find someone knowledgeable about wiring and have them check the breaker panel and the size/condition of the wire in the outlets. They may be cutting corners that the building inspector and the fire marshal would like to know about.