There is a on line system for easy application.first you subscribe to anti Covid insurance(cheap),then you continue on stage 2 on the same software and you have the choice for health insurance between approved by Thai authorities.That's all.Easy.
If you are cautious,you can also subscribe on top of that,a TRAVEL health insurance,you can choose on international market.Brands like APRIL,CHAPKA...
Yes,coming from outside is different.You need COE, and for COE you need anticovid ins,then next step as usual health insurance.For newbies it's not very clear.But not difficult.Except if you are more than 70 y.o.Read small characters.Difficult.