If you are OK with cold temperature, Nepal would be the best option for celebrating Christmas and English new year. It is a nice destination to spend your holidays.
The best mountain places are Shimla, Sonamarg , Auli , Manali, Kutch, Tawang, Binsar ,Leh , Cherrapunjee, and many more .
and the best beach places are Kerala, Havelock Island, Gokarna. goa , Pondicherry, Andaman and Nicobar and many more.. i hope this helped you . enjoy you trip and be safe .