@Mike *****
Fly to Thailand without any visa and enter Thailand “visa-exempt”. According to your profile, you are from the U.K., so you are entitled to enter Thailand visa-free.
You will receive a 60-days stay permit stamped in your passport.
***The only thing you have to watch out:
Your airline might ask you for a proof of onward travel out of Thailand within the first 60 days you will get stamped in, or they won’t allow you on the flight.
You can solve this minor problem by either buying a cheap Air Asia one-way ticket Hat Yai to Kuala Lumpur for 53.- USD, or buy one of those “fake” tickets called “onwardticket” which are a “flight reservation” valid for 48 hours.
Both are just for the show and you could throw them away after having arrived in Thailand.
Regarding the cheap one-way ticket to Kuala Lumpur or to Siem Reap Cambodia or Vientiane, you could actually USE it to make a “border run” out of Thailand and back, if you book it as a both ways ticket!
***You should NOT (!!) apply for a 30-days extension on top of these 60 days. That’s throwing 1900.- THB away, throwing money away - and it is NOT needed when you only want to spend 120 days in Thailand!
Watch out for BAD advice here from the many “barstool experts” !!😠😡😕
Just do a “border bounce” to a neighbour country, re-enter Thailand “visa-exempt” and receive another 60 days stay permit
(even if you did a 30-days extension, you would still have to do a border bounce, dig? So the 30 days extension saves ya nothing but costs you extra 50.oo Pound Sterling)