I couldn't answer this myself - never been there. But my friend, Fred, is visiting this afternoon and he just recently returned. So, I'm turning this reply over to him.
Two days in Bangkok is not really enough time to see much. I spent an entire week there and still felt that I could have spent more time. You really need to go to Wat Pho and the Temple of the Emerald Buddha. I am sure that you will be overwhelmed by both. I stayed in the middle of Chinatown which I highly recommend. I think it is probably the most atmospheric part of Bangkok. I stayed at the Royal China Princess Hotel. It was very reasonably priced and included an extensive breakfast with the room. It is also within easy walking distance of the water taxi on the Cho Pharya river which is the fastest way of getting around Bangkok. It is also the cheapest. NEVER NEVER use a cab except getting to and from the airport. You can get stuck in a traffic jam and never see anything.
You need to remember that November is the end of the monsoon season so it is not only possible but likely that you may get caught in some torrential downpours. Be prepared. Also keep in mind that bathroom facilities are not like those in the west. frequently nothing more than a ceramic hole in the ground with a bucket to rinse off. Toilet paper is rarely seen!
I also spent a fair amount of time in Chiang Mai. It is completely different than Bangkok. There are five different hill "tribes" there who are completely different than the usual Thai people. It would be best to arrange transportation to what you might be interested in seeing. Here isa good source: a_kanchaiya@yahoo.com.au. The wife's name is Noi. She is very experienced at setting up tours of the region. Her husband, Thep, can drive you arround. She set up a visit to one of the hill tribes, the Hmong people, for me, bamboo river rafting and elephant riding.
DO NOT MISS DOI SUTEP MONASTERY. It is up on the mountain overlooking Chiang Mai. It is perhaps one of the most spiritually interesting places I have been. Noi speaks English extremely well which is more than I can say for most Thais. Everyone is extremely hospitable in Thailand however. I do not know how adventurous you are with accommodations. However, I stayed at a small B&B in the middle of Chiang Mai called Seven Suns. It was quite popular with European backpacker types if that is your cup of tea. Noi can also recommend other accommodations.
Personally I would get to Chiang Mai by air rather than the train. Bangkok Airways will get you there and back relatively inexpensively. Get on AirGorilla.com to look up fares. Gorilla is sort of the clearing house for southeast asia travel. I highly recommend them. I booked over sixteen flight segments through them on a variety of airlines. Again, I do not know how much time you were planning to spend in Chiang Mai, but a couple of days certainly won't do.
November is also the month in which the biggest festival in Thailand other than the King's birthday, which is December 14. It is called Loi Krathong or water festival. It is held on the first full moon in November. Sorry don't know when that is this year. It is best to be either in Chiang Mai or Sukothai for that event. It is a truly magical experience you will never be able to describe to anyone who does not experience it first hand. Noi took me to her Buddhist temple for Loi Krathong. It was very moving.
You also expressed a possible alternative to Chiang Mai of going to a beach. I went to Phuket Island. It was one of the locations where 8,000 people died with the tsunami. I was there one year after the tsunami and you would never guess that it had happened. I do not recommend Phuket. Way too touristy for me. Too westernized and tacky!!! I would recommend staying on the north side of Phuket and spend your time in Phang Nga bay. Less touristy and very quaint. Or you could go to Ko Samui. I am told that it is a lot like what Phuket used to be like before it became a tourist magnet.
Personally I loved Thailand and its people. I would go there in a heartbeat. You have an amazing adventure ahead of you. Thailand is one of the most exotic places you will ever travel to. Great traveling!!
OK, Suzanne is back now. As you can see Fred had a wonderful time on his trip and loved every minute of it. If you want to "talk" more to Fred, let me know and I'll send you his email address.
Have a wonderful time!!
Suzanne