I am back in Japan as well (Kobe now). To save on air-conditioning, I missed a very hot summer here ;-)

For winter, some heater has to be bought indeed. Winter temperatures do not go below zero much, but high humidity makes you shiver. On weekdays, I usually come home late like you. Last winter I often kept heater fan on low at night, to keep myself just about healthy - I'm going to do better the coming season.