I think the best place for what you want is Thailand. You can choose from Phuket or Ko Samui or one of many other islands, and they all have nice beaches and good nightlife at a very reasonable price. There are other places in Asia that have warm December weather, but Thailand’s tourist infrastructure is better than the others so it’s just much easier to get around and do what you want. Let me know if you have any other questions. -Roger
The traffic in Bali makes sightseeing notoriously challenging in June through August, but November is less crowded so it's a good time to come and spend a day in Ubud or even take a tour of the towns along the northern shore. In fact, if you want to avoid the huge Kuta crowds altogether you should consider basing yourself in the Lovina area of the north shore. It's as lovely and charming as the whole island was 20 years ago, but that may not last.
For traditional holiday atmosphere, think about Rome or Vienna, with Christmas markets, nativity scenes, and decorated cathedrals. In Edinburgh, they know how to welcome the new year with several days of celebrations culminating in New Year’s Eve. For travelers seeking a wintery destination, Tromso in Norway has skiing, reindeer, and a chance to see the Northern Lights. Bundle up for a dogsled tour or join a whale watching excursion.
Southeast Asia is easier to deal with, and there are cheap flights connecting in the Middle East and landing in Bangkok, Kuala Lumpur, and Singapore. Each of those is a very interesting city, and there are many smaller places to go in the same region. In Malaysia there is Penang and Melaka. In Thailand there is Chiang Mai and quite a few others in that area. In Laos you can visit Luang Prabang, which sounds like it could be a winner for you. And there is also Siem Reap, which is home to the amazing Angkor Wat temple complex.