not only Nakhon Si, also Koh Samui Immigration does not allow a fixed account. Now don't fall out of your bed explaining that Koh Samui is in the sticks 😂
I get 1.2% interest for the 800,000 THB in my SCB savings account, which I use for my yearly application to the next extension. Not too bad an interest for the parking ticket which enables me to live in a country where my Euros have double a purchase power 😉
it's not only the offices in the sticks, many offices in the South like Nakhon Si Thammarat or Phang Nga don't allow fixed accounts. I have seen reports
then you were lucky to have met with an Immigration office that allowed these steps. Be aware not all Immigration offices of 85 offices in Thailand will allow the first one-year extension based on the 12 months of transfers of 65,000 THB
unfortunately, the Phu Nam Ron border is closed for foreigners since several years. Cambodian land borders are closed as well. So since you won't fly because of your dog, there really isn't much choice. Either use a company that gets you to Laos, which requires a 10 hour one way trip, or, take a taxi to Hua Hin and visit LIME tours. They get you to Ranong/Kawthoung by a 5 hour van ride, provide a meal and the border run across to Myanmar. It is the only border with Myanmar which foreigners can still use.