What are the steps to apply for a Retirement Visa (O-A) for Thailand as Australian citizens planning to settle in Koh Samui?

Previously I would have said get the OA in Australia before coming here as you can get almost two years out of that visa and it has the advantage of not having to move a big chunk of money over to Thailand to sit in a low interest earning account. However now with the OA you need to have health insurance for both inpatient and outpatient pre-paid for the whole duration of your stay

Many Australians in Thailand are now choosing to instead enter Thailand visa exempt (45 days) or on a single entry visa (60 days) while they apply for the non O visa here, and wait for their 800,000 baht to season for 2 months in a Thai bank. In order to avoid the compulsory insurance requirement

Apply for the O A in Aus. I went through the Canberra Thai embassy and they were great. Once I had all the paperwork which you have post off 3 copies with passport, mine was approved the same day

The O-A multi-entry from Australia does not require you to have any money in a Thai bank account, only sufficient funds in Australia to meet the requirements. If you use the multi-entry wisely you can get 2 years from that visa. I would suggest that you look at the O-X from the Thai Consulate in Sydney, not Canberra, far better visa for long term.

now as far as IF you could enter on a 45 day visa exempt entry without proof of onward travel that is going to depend 100% on your air carrier, 😮 Some airlines have a policy that if you're flying here without a valid visa in your passport (entering visa exempt) you need to have proof of onward travel within the number of days you will be stamped in for, BUT some don't have that policy so check with your air carrier

If you manage to board your flight without onward travel you won't have any issues stamping in here at passport control visa exempt

If you are going to get the OA visa (or the OX 10 year visa) you have to do it in your country BEFORE you wing your way here.

The OA is not sold inside thailand. You would need to enter the country apply for an O visa for 90 days, by meeting the proof of funds in a thai bank account in your name only) wait the review period, get the Non-O visa, then after the funds were in the account for 2 months you could apply for the year extension

Unless you're BOTH going to meet the financial requirements and apply for separate retirement visas here (the Non-O and year extension) you will have issues because inside the country they do not issue Non-O visas for trailing spouse to people on retirement visas

I'd say get the OA (or look in to the ten year OX visa) before you come here from the thai consulate in your country. That OA visa gives you almost 2 years of stay on a visa valid for a year if you use it correctly.