What is the best visa option for a 6-month stay in Thailand, considering travel to Vietnam and Malaysia?

Then you are taking about 2 seperate visa periods, and at least the first one can be done with a 60 days touristvisa + 30 day extension at the Immigration.

Depending on you passport, you can apply for the touristvisa online from your homecountry through the thaievisa.go.th. website.

For the 2. visit, you may be able to apply for that directly at the Thai embassy in the country, you visit between the 2 Thailand visits, or you could choose to “only” stay 60 days, with a 30 day visa excempt + 30 days extension.

It make a huge difference, that it is 2 seperate stays in Thailand, instead of 1.

But it is also depending on which passport you have.

@David ***********

it's possible until it's not. All depends on the immigration officer you're standing in front of.

@David ***********

that depends on your embassy. As Kool mentioned you can only get it at the Thai embassy in your home country.

But you're probably not going to be let into the country after you try entering again as a tourist after 6-9 months already in the country as a tourist. You can't live in Thailand without a long term visa.