My mother and I are thinking about flying to Beijing in late December, visiting Xian and ending in Shanghai- flying home from there. Could we do a river cruise along the famous Yangsee river along the way? IS it too cold to visit and enjoy? If this is a "now or never trip" would it be OK in winter? Any ohter sights that are must see along the way? It will be a 2 week trip. Any tips appreciated!