What visa options are available for an Australian living part-time in Thailand with multiple entries each year?

STEP-BY-STEP DO-IT-YOURSELF INSTRUCTIONS -- APPLYING FOR RETIREMENT STAY AFTER ARRIVAL IN THAILAND (Must be over age 50): i. You may arrive either Visa Exempt (currently 45-days), or on a 60-day Tourist Visa. ii. Then, immediately after your arrival, you must promptly open a Thai Bank Account, and transfer 800,000 Baht into Thai Bank Account (if married, some Immig. Offices like CM, accept Joint Account with 1.6 Mil. Baht. Also Note, that either Passbook Savings or Fixed Deposit is acceptable, but not Investment Account. Finally note, that some Immig. Offices, but not all - e.g. CM, require proof of foreign source of funds. WISE is an inexpensive, easy & reliable service to transfer funds). iii. Then, you apply for a 90-day Non-O Visa at local Thai Immigration Office. If on Visa Exempt, you use Form TM87, if on Tourist Visa TM86. You are required to apply with minimum 15-21 days remaining on permitted Stay, depending on Office (Chiang Mai, requires 21 days). Requirements: TM87 or TM86 (Note: Fear not, only 1-page Form simple to fill out in English with only basic info., name, address, passport info., arrival info, and stated purpose: "For Retirement"), Must be Over Age 50, 2000 Baht, Copy of all relevant pages of Passport (i.e. Facepage, and Entry Stamp); copy of TM30 (that is the required arrival form that is either completed by your Hotel or Condo, or you do yourself at Immig. Office w/i 24 hrs of arrival); copy of proof of residency (Rental Agreement, or Hotel Reservation -- some offices may not allow if only staying at a HOtel); and most importantly proof of the money in Bank (Copy of Bank Book, and a certified Letter from the Bank usually costing 100 Baht). Above is all simple and straightforward, so no need for spending money on a Visa Service. iv. If all docs. in order, Immig. Office will put a Sticker in your Passport that you are "under consideration", and a date to return to pick up your Visa Stamp (prior to your Stay expiration). v. Next, when you have 30 days remaining on the Non-O (and your Bank Money has "seeded" 60 days -- i.e. stayed on deposit), you go back to Immig. Office to apply for the 1-yr Retirement Extension. Requirements.: TM7 (Req. for Extension of Stay); 1900 Baht, and all other same docs. as above (newly updated of course). And, you will receive 1-yr Extension of Stay -- usually same day, if you arrive in morning. Note: For both processes above, your Bank Passbook Balance must be updated same date as application, and the Bank Letter should be no more than 7 days old -- easiest just to do both same day just before going to Immig. Office). vi. Finally, you should/must get a Re-Entry Stamp -- easiest/best to just do immediately after you get your 1-yr. Extension stamp. It can be single Re-Entry for 1000 Baht, or 3800 Baht for unlimited multiple Re-Entry. The Re-Entry Stamp allows you to leave and return to Thailand, without invalidating your 1-yr Extension. If you fail to do that, then your Extension of Stay is nullified, and you must start the process again. (IMPORTANT: If you want or need to leave Thailand while on the initial 90-Day Non-O, same thing -- must get Re-Entry Stamp.). Hope that is all clear.

I already do what your thinking of doing. I have been 2 and 2 for 8 years. Decided to stop risking an IO questioning me and obtained the retirement OX visa in May 2022 to avoid any future hassle

You should look into a long term visa (6 month METV, etc) because all it takes is one over zealous I/O to put an end to your frequent trips in/out…on the METV there is no limit to how many you can get in a row

By any chance are you over age 50? If so, then all your best solution would be Retirement Visa (i.e. presuming you do not work in Thailand as your Post indicates you do not).

If you're only staying two weeks at a time you're probably going to be fine. You might run into an immigration officer who wants to hassle you eventually. Maybe have some evidence of you working in Australia so if asked you can show you're working overseas.

Will probably be fine without a visa but you could eventually run into issues.

You could apply for multi entry tourist visa that's valid for 6 months, and you'll be stamped in for 60 days each time you enter.

If you apply for METV you need to show a flight to Thailand, a flight out of Thailand, and another flight back into Thailand.