Terry I went thru what you're looking at now some time ago, by that I mean wanting to make sure Mrs Worx had top health cover recognized by the best hospitals for in and out patient. I was working away a lot back then and it gave huge peace of mind knowing if the shit hit the fan health wise, she was well covered.
So what I did and you should too, is find a reputable insurance agent to discuss this with. We have such a guy in Pattaya that most long term expats use for all their insurance needs, a high profile Englishman who's company has been around forever (at least 20 years that I know of) and he's a straight shooter. There must be such a person/company in Bangkok, there'd be several, and you should ask around the Expat community to find out who they are.
After a meeting with him outlining the desired coverage, he presented 3 options from 3 different insurance companies and ultimately we went with Pacific Cross. The main reasons for this are they were his top recommendation, and I've been with them since the 80's with no complaints over their handling of the few times I've had to pull the card out while checking into a hospital. In fact, they've been fantastic.
How much this will cost will depend on many things which should be explained to you in detail by your broker (age, pre-existing conditions, past illnesses, exclusions, level of cover, etc) but to give you some idea Mrs Worx's policy costs about 37k Baht per year. That's top-tier level that would cover pretty much anything with in and out patient included.
The peace of mind that comes with this is well worth the ticket price. The Mrs is in excellent heath but you know anything can and will go wrong, plus Thailand is such a dangerous place on the roads (she has a car and a motorbike) so if she's in an accident the card in her purse will ensure she's taken to and treated at the best hospitals in the area.