Don't underestimate how much its going to cost to live comfortably in Thailand..
Yes, I am certain its cheaper than Canada and most developed western countries but you may be surprised how quickly you can burn money especially if you are living in a very popular tourist location paying tourist/Forienger premiums on everything..
Just manage your budget expectations very carefully would be my advice..
Phuket is one of the most expensive places in Thailand for foreigners (Tourists and Expats) and so are most of southern islands like Koh Samui..
If you are thinking of living on a budget then Phuket or anywhere in the south is a very poor choice..
Mainland beach locations are generally cheaper than places like Phuket or Koh Samui etc..
You may want to consider Hua Hin as an option as it very popular with retired Expats and foreigners staying long term and has excellent amenities and infrastructure and only 3 to 4 hours from Bangkok and a nice beach location..
You can get to Hua Hin by Bus, Train or even taxi from Bangkok.
Lots of long term accommodation options available in all price ranges.
Or if you want something quieter and more laid back then perhaps Cha Am just a little North of Hua Hin or maybe Prachuap khiri khan which is south of Hua Hin..
If you are planning on long term living in Thailand then you really need to do some research and visit a few places to be certain they are right for you.
You need to exit and apply online for another Vietnam visa..
Not sure what passport you hold but you may be better off going to Cambodia as they have slightly more friendly visa options and visa on arrival for most passports.
Phnom Penh is nice city so I suggest you check that out..