List of all insurance companies in Thailand.
http://www.buriramexpats.com/health/insurance-companies-thailand/*
Many English people insure themselves with "BUPA" insurance company but be aware there are 2 kinds of "BUPA" insurance;
International and the Local-Thai BUPA insurance.
The differences are in the coverage of body injuries and of course the rates are very different as result.
Make research.
The most important thing is the network each insurance company link to, and the hospitals they are connected with. As a person want to insure yourself, you would like to insure yourself with an insurance company with the best hospitals network.
IE; In worst situation you get the better hospitals. which in other insurance company you may not be entitled to get treatment in there.