You could also take a very cheap insurance, starts around 9.000 thb a year if I'm not wrong ( with high deductible of about 200.000 thb with OP cover that qualifies for the non OA but in fact is useless ) and take another good insurance to use for real need Then you can keep the non OA without the 800.000 in account. Or switch tot non o as said before For the cheap oa insurance, and all others you can take a look at
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They have offices in Phuket, Hua Hun, BKK and Pattaya