If I can recommend one thing for aspiring teachers in Japan, when winter comes close, get some HeatTek from your local home center. It’s fairly cheap (mine cost about 780¥ per shirt/pants) and it works really well when you are active. It’s like Spandex, but a little less stretchy and you wear it under your business clothes. If you have a sedentary job, then it doesn’t work as well (but if you’re too hot, then just relax and it lets you cook off). Just casually moving around the teacher’s room gets me nice and warmed up! Love this stuff. If you don’t have access to a home center, then it is also available on Amazon.co.jp.