여기는 어떤 곳인가
No country on this site makes staying easier. An ordinary business visa extends for twelve months at a time, indefinitely, with no income requirement and no employer, for a few hundred dollars; the retirement extension does the same for anyone over 55. Two things to weigh against that: none of it ever becomes permanent, and serious illness means a flight to Bangkok.
절차는 이렇습니다
Enter on an ordinary (E) visa
Ask for the ordinary visa, not the tourist one; only the ordinary visa extends.
Take a twelve-month extension
A few hundred dollars, about a week, and repeatable without limit.
Buy evacuation cover, not just health cover
The realistic plan for a serious illness is a flight, so insure for the flight.