Also because of your age, if you've got no underlying health issues you can get health insurance quite cheap, but do your research on it before committing to a policy.
Go down the DTV route, you can apply for the visa in Australia on the e-visa portal and all it'll cost you is the visa fee, which I believe, depending which country you apply for it in, it's anything between the equivalent of 10k & 11.5k thb.
You can apply for the DTV., with 500,000 THB equivalent in a bank account in any country. Applying for the DTV., through the Soft Power route, you need to book in either a Muay Thai or Thai language course. As far as I'm aware from other posts, there is no minimum time of enrollment on any of the Soft Power application procedures. You say your only forty, so if your into keeping fit Muay Thai would be a good way to go and even if your not, just doing the fitness part of Muay Thai will get you super fit in a month or two, depending on how many times a week you select to attend. No mandatory timeline for attendance, it's Upto each individual.
If people haven't ever overstayed, which I did three times, although two times were only by 1&2 days. The other time was 3 days and that was because I'd put my passport with all required documents into the Nigerian Embassy, off Sukhumvit to process a visa and work permit. I submitted this application on a Thursday and before I submitted my passport I told them I need it back by at the latest the following Monday. They said I could pick it up on the Monday morning. When I went back on the Monday, there was a notice on the gate of the Embassy, saying this Embassy is closed until Thursday for the King of Thailand birthday celebration. So there was me stuck in Bangkok for three days which would of made me overstay 3 days. I went to immigration in Bangkok, explained to a lovely lady IO., what had happened, she made a note of it, gave me her personal card and told me if you have any problem with police or any other officials, get them to call me and I'll put it right for you. She said when you leave you'll have to pay, at the time it was 200 baht a day, so 600 baht. Got my passport hopped on a plane to Udon Thani, straight to Vientiane on the bus, paid the fine and did a border bounce and that was on a visa exempt thirty days entry, when I had the problem. So immigration in Thailand, if you've got a genuine reason for an overstay, as long as it's not an abusively long overstay, they won't or shouldn't hold it against you.