I am Canadian, Canada and Thailand have a reciprocal fiscal agreement. Income is taxed only in the country where the pension comes from, for me, in Canada. There is no double taxation. You have to do your homework and find out if there is a similar fiscal agreement between Australia and Thailand.
In my case, they asked for a translation of my passport to Thai and an affidavit (also translated to Thai) saying that I am free to marry in Thailand. These 2 documents needed to be certified by the Thai ministry of foreign affairs. Just got my docs from the attorney (translator) who managed the MFA certification.
You get a 50 day on line on the the embassy website. Once in Thailand, you go to an immigration office (in any good size city) and you ask for a 30 day extension…
this is what I just got from the Thai Embassy: Financial evidence showing monthly income of no less than 65,000 THB or having the current balance of 800,000 THB, e.g. bank statements, proof of earnings
Both non-Thai national applicants must be 50 years or older.
Must meet the following financial requirements:
Have at least an 800,000 THB deposit for at least two months before the visa application.
A monthly income of at least 65,000 THB.
A combination of security deposit and annual income of a total of 800,000 THB.
Non-immigrant type “O-A” visas are required to have a health insurance policy with a minimum coverage of 100,000 USD, including treatment for COVID-19.