The coldest time of year here always seems to be january and february. That's when I start blocking my windowpanes with cardboard and pulling the more tender plants off, overnights.
I also try to remember to mist the houseplants- this is better than overwatering to counteract dryness, and helps against spider mites too. Some plants don't like this- jade, geranium, cyclamen (can get crown rot), african violet (will get mold on leaves), creeping charlie. Poinsettia and pothos- sometimes. The ones that definitely need it: schefflera, coleus, spider plants, dracanea, palms, croton, avocado, and especially the fern. That big beauty still gets special treatment- I often carry it into the bathroom during bath or shower time. The croton was showing signs of spider mites- two leaves dropped before I noticed- so I've moved it away from the window base to sit next to my avocado, where I see it more and won't forget to mist. Plus it won't spread mites to all the other plants here further from the group.