As long as someone knows the rules about overstays, as the questionnaire asked, stating that their visa expired on the 8th and they were flying out on the ninth, the chance of an encounter with an official (police) is about as much a risk as being in a plane crash.
Well your plane might crash also. Depending on what sort of person you are, why or how could you get involved with the police. Incidentally when I lived in Udon Thani, I was stopped on a regular basis by the police on roadside checks for driving licences and at the time I had a tatty old British licence that didn't contain a photo. Not once was I ever asked for my passport and one time I was pulled up for speeding between Korat and Khon Kaen by radar. They told me I was doing 140kph and the limit is 90 kph., which to be honest I wasn't aware of. Anyway wasn't asked for either passport or driving licence. Just fined 200baht.
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.