Just to throw a bit of an idea that you would need to confirm.
The embassy in Canberra, Australia may still offer a non-o dependant visa, alongside the 90 day non-o. Based on retirement.
This was just a few months ago.
See attached:
You can apply for a Non-Immigrant "O", "O-A", "O-X"/ Retirement Visa and her husband can apply for a Non-Immigrant "O" to follow his wife to stay in Thailand. Please visit this website for further information about Thai Visas: