So you can enter visa exempt, 60 days. During that time convert to a single non-O, 90 days, at immigration and in the last 30 days of that go back for a 12 month extension of stay.
Alternatively, you can apply for a single non-O e-visa (retirement) whilst you are in Australia, that cuts out the conversion step.
Either way you'll need 800k in the bank when you get the non-O.