@Ellie ******
brought up another option, seeing as you are over 50 you could apply for the year-long, multi-entry Non-Immigrant Type O-A (Long Stay) visa either from the thai consulate in Phnom Penh (because you have legal residence in Cambodia) OR when you're back in Australia from a thai consulate there that issues it
That visa would give you unlimited entries for the year it is valid for and each entry gets you stamped in for a whole year.
Check the websites of the consulates to see if that visa is an option for you