Standard bank letter is normally valid for up to 7 days after it’s issued. Generally it’s anyway recommended to try to open a bank account in the area where you physically will stay, as you’ll have to pay a (small) fee for withdrawing in other districts.
If you’re married you can apply for a 90 days Non O visa based on marriage and yearly extensions of stay with a affidavit letter confirming income from your German (Austrian or Swiss) embassy in Bangkok.
Requirements for Non O visa based on retirement if you’re passed 50 years is minimum 1713 euro a month.
Ok, it might be different than an Norwegian then, as there was an official statement today confirming that your travel insurance still is valid as long as there’s no on going evacuation order in the area where you stay.
Ok, at least not the embassy in London, and normally it’s sufficient with current balance at date regarding funds for a Non O, also for a Non O in country Thailand.