Heater? Heated seats? Of course; in addition, try leaving the sunshade open on those sunny days to take advantage of solar heating.
Very easy.....I live in Florida!!
I use both heater and heated seats. Unfortunately on cold days, I have to drive about 20 miles before my car gets warm inside. Probably because the heat source is very small and the warm air has to be pumped from behind the driver to in front of the driver before it enters the cabin. Having a cabriolet, I don't have a sun shade for solar heating, just an openable roof - GREAT in summertime. If I open the top in winter, of course warm air rising would freeze the inside in a heartbeat - NOT so good in wintertime :-)
We use the heated seats for about 5 minutes, usually on the low setting. The heater kicks in with warm air, in fact too warm, rather quickly and we have to open a window and turn down the heater. Of course, I am talking a cold day in Southern California, where the temperature in the morning may drop down to the low forties. That is cold for us.
I live in Texas. I think I've used the heater once this winter and for only a short while. Most of the time, my A/C is on or the entire system is off, not blowing!