What are convenient destinations for an Aussie to exit Thailand while applying for a retirement visa after overstaying a tourist visa?

I am Aussie intending to apply for retirement visa. Overstayed on my tourist visa a couple of days, and while extending it l find now cannot apply for O visa while on a visa that has been overstayed. Was told must exit country and reapply for O visa on new tourist visa. I wonder if you might recommend convenient destinations from Bangkok. Long bus trips are not as easy as the used to be and I was considering a flight to Phenom Phen. Is this a good border bounce, in the vernacular? And do you know if I will be required to have an exit flight ticket when I re-enter Bangkok by air? I will take a bus to avoid that kind of situation if a land border cross is more convenient.

I have to say it is pretty handy having you guys and your experience to call on. Cheers to you for that. And I will happily turn that into a few beers if given the chance