And "ditto" for Wuxi.

The previous poster is on the mark. Long underwear, thermal socks, a very, very warm flannel bathrobe.

I hope that your apartment has an air conditioner with a heater (not all do). You will need it. And the Hangzhou winters set in mid-November and can last until the end of March (with wet, heavy snow, fog and cold, driving rain at that date).

He's so true...you will never, ever be as cold in China as you will be in a Hangzhou / Suzhou / Wuxi winter. And gray and bleak. Mercifully, they are seasonal, meaning November / December / January / February being the worst. It can, and I say only it can, get better in March. April is definitely spring, for a week or two, before it becomes hot and humid until the rainy season sets it.