What is the best visa option for a retired expat returning to Thailand from Cambodia before leaving for Australia?

Hi, my retirement visa expires on 7th October and I am not renewing it as heading back to Australia for 4-5 months at Christmas. I am going to Cambodia on the expiry date for 2-3 weeks. Is it a better option to go to the Thai embassy in Phnom Penh and get a 60 day tourist visa to get through to my departure date, or. can I simply get a 30-day visa on arrival and then a further extension at Jomtien immigration to cover the remainder of my stay? I am aware that I may need to show ticket out of Thailand and 20,000THB cash if requested when re-entering.

Thanks for any responses.

Regards

Mauro