The best places in December with good weather and that are inexpensive and also fairly close to India are Sri Lanka and Thailand, and they are both mentioned in the article above. Sri Lanka is obviously closer and you have many nice and scenic areas in the hills as well as the beach areas along the southern coast. But Sri Lanka has many similarities to India, as you may know.
Yes, I’ve been to all of the Nordic countries, but mostly during the summer months. However, I know that those Northern Lights tours are popular and well established. On one hand, you know you’ll be visiting areas where there is only a bit of sunlight in the middle of each day, so it won’t be great for general sightseeing. But the cold months are also the best Northern Lights months, and if you want to see them then it’s your best bet.
I totally agree about the solo traveling thing being down to luck in many cases. Right now I’m on a long trip around Europe again, and from one night to the next I might meet a bunch of interesting people, or be sitting there alone in a sea of locals with no interest in chatting with foreigners. At least in a place like Goa, everybody is on holiday, so I’ve had good luck meeting people.
If you can, try to stay at a hotel or hostel that has a kitchen which guests are allowed to use. You can also elect to find home-share style lodgings, as people often rent out their homes during peak vacation times for tourists to use. Once you have a kitchen, you have control over what you purchase and what you eat. An added benefit of this style of travel, other than the fact that you can stick to your Keto Diet effectively, is that you get to experience the local side of life. Going to grocery stores, choosing from local ingredients, and cooking for yourself will help make you feel like you’re a part of the culture, instead of only a visitor.
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.