you keep on repeating this assertion with zero evidence as if it’s what happens with all agents. It is extremely rare for that to be the case and certainly never the case with any of the numerous agents in Pattaya who all deal with Chonburi immigration.
Gillian Dodd A re-entry permit is easy to get at any Immigration Office, or even at the airport when you leave if you’re not going to be near an Office.
Again, you’ll need to get the timing right as regards when you want to get an Extension.
At what stage in your trip do you want to go to Brisbane?
If you time it so that you return to Thailand with 30 days or fewer left on your total trip then you can get a Tourist Visa for your first entry and then just enter Visa Exempt on your return from Brisbane. Eg 50 days in Thailand, 10 days in Brisbane, 29 days in Thailand.
You could even do that earlier (as the Visa Exempt can be extended) but might have an issue with the airline at BNE.
Simplest way is probably to get a Non O visa ‘for Retirement’ from the Thai embassy in London and then get annual Extensions of Stay from the Immigration office in Thailand.
You’ll need 800k baht in a Thai bank account for the Extension.
You can get a Non O ‘for Retirement’ from London fairly easily - all online now. You’ll need to be getting a pension or have £10k in your home bank account for 3 months. You will need insurance but travel insurance will do as long as it meets the minimum requirements. It only has to cover you for 3 months as the visa gives you that long on entry.
You will need 800k baht in a Thai bank account to get your annual extension of stay in Thailand at the end of the 3 months. You won’t need insurance for this. Some offices insist on that being there for 2 months beforehand but others don’t.