I'm living in Thailand now! We moved here a few months ago, and am torn between loving it and being a bit lonely. DH is working PT in schools here as well (I'm the main wage earner).
So here's my observations:
There are a few good international schools in Bangkok and some really hi-society Thai ones which pay well if you have been recruited from abroad. I have no idea about schools in Chaing Mai, though. The forums already mentioned are great places to get contacts, info etc.
Its much harder to get a good package once you are here (ie ones with flights home, accomodation allowance, medical, etc) - you tend not to get such good deals, because they tend to assume that you already have an expat package from your partners job if you're part of a couple, or that you are earning just to travel if you are single. So apply from the UK rather than just turn up!
Teachers are really well respected here - especially by Thais - so the experience of being a teacher is so very different from the UK.
But teaching in Thai schools is really different - lots of focus on learning by rote rather than critical thinking. Discipline is hardly ever an issue, but getting pupils to speak up can be!
CM is gorgeous - very cultured, lots to do. But has fewer opportunities workwise than Bangkok.
BKK is dirty, smelly and poor in parts, and vibrant, exciting and dynamic in others. As is Thailand as a whole Some people love it, some hate it. If you are really serious about it, come over for a couple of weeks when you have a better idea of what kind of money you might earn, and see what that buys you in terms of lifestyle. If its Bangkok you are interested in, I'll happily link you up with some people and show you around if you want!
Thailand is a cheap place to live if you want it to be, expensive if you want the expat dream. I pay (well, my company pays) over 3k a month for my apartment, but its huge - 4 beds plus maids quarters, massive reception rooms, vast balconies off all rooms, nice marble bathrooms, and in a great location which is really central (I can walk home from work if I want) but also really quiet.
The building has 3 pools, a gym, squash court, pool room, table tennis room, sauna (don't get why you want a sauna here!) and games room, as well as a covered and an open children playground. So fab facilities. We decided against a house for security reasons as well as the fact that condos are easier to service, maintain (insects and snakes can be an issue in a house!) and you get to meet people. I can recommend a property website if you are interested.
Food is cheap, unless you like to live on a diet which includes lots of cheese, cream, potatoes and lamb, in which case you may need to sell your children to afford it! But fish, chicken, pork, fresh fruit and fresk veg all good value - especially fish. Quality is good as well - really really fresh, and good stores (Tesco is massive here) as well as fresh markets. Wine is exorbitant - except Thai wine which is undrinkable. So we tend now to have one bottle a week, for which we pay around the 20 quid mark (and that buys you Lindemans type stuff, nothing fancy) and drink beer if we are going out.
Food allergies and intolerances are hard to cater for - especially if a nut allergy is involved. They aren't understood, and everything has nuts or nut oil in it. So if that's an issue for your family, think again.
Electricity is astronomical - we spend about 250 pounds a month (and we don't use the aircon that much) - but water and gas are cheap (about 15 a month for both).
Cable and mobiles are UK pricing, as is broadband. Crap TV even on cable, but DVDs supercheap (pirate - its actually pretty difficult to buy kosher DVDs here).
You acclimatise fast, so don't worry about heat, although you will be hot a lot of the time. DD has coped better than I have! But you do tend to play indoors more than outside - outside is beach or pool rather than park (there isn;t really a Bangkok equivalent of local park around the coorner, but there are some nice large parks a la Hyde Park).
BKK has some nice stuff to do with kids, but some of it is expensive. My DD loves just hanging at the mall - she's 2.5 and think escalators are fab! But we struggle a little with the fact that going out for a walk isn't that easy (too hot, too dirty, nowhere to go) - the pool comes in handy though, especially as a place to meet other people. You just adapt to a different way of life.
Schools are great for kids but very expensive - UK private school pricing. But unbelievably well equipped, staffed etc. Very international, so lots of cultural opps.
Disease - just keep jabs up to date and use child-friendly insect repellent when out and about. Malaria isn;t an issue in BKK, don't know in CM. Dengue is a problem everywhere (daytime mossies are the culprits here). Other than that, just practice good hygiene, and you should be fine. You will become obsessed by foot health, esp in the rainy season.
Ah yes, the rainy season. Not as bad as I remembered, but a bore nevertheless. Roads clog up, traffic grinds to a halt, but in BKK you have the skytrain and the underground, which helps.
Weather is otherwise fab - we spend about every 2nd weekend at the beach (villa rather than hotel)- easily doable.
Cars are astronomical to buy, leasing is better, and I have a driver, so only drive myself at weekends and out of BKK. Taxis in BKK are so cheap - less than a pound for an average journey.
Home help can be very cheap - 350-500 average for live in help - nanny/maid. I pay a lot more, but many don't, so depends on what you need.
I have found it hard to make friends though, and I miss my friends and family terribly.
What else do you want to know? Feel free to ask!