Korean weather from December to January
The most important thing in Korea is to have a thick coat. There is at most one sweater inside. Seoul has that say about the weather. That is to say, after a few days of being very cold, there will be a few days of warm sunshine. Some places in Korea are very cold. Seoul doesn’t really need snow boots. Recently, girls are even more afraid of the cold. They don't even wear stockings anymore. I was so cold looking at it. But even if there is snow, it will be cleared away before you go out. Moreover, buses and subways are equipped with heaters, which are very warm. You can even wear short-sleeves at home. Bring a pair of warm pants if you're going skiing or hiking. Just a pair of pants is enough for Seoul.
Otherwise you will be too hot to death when you get to the house,