You must check that the insurance meets the requirements set by the embassy here. If it is not a Thai insurance policy, I guess you must fill out the certificate for foreign insurance.
Okay, that’s a strict embassy. If you want an approved health insurance, you’ll either have to choose a company from the list or apply to have another one approved using the form from the attached link.
Then you need to book your ticket with a return flight if that suits you. Otherwise, you can just get a cheap throwaway ticket out of Thailand.
You’ll also need to include the booking. If you don’t want to book much of your stay now, you can use a hotel service that allows free cancellation after the booking has been confirmed.
If you are renting the property, the responsibility lies with the landlord. However, you may personally visit the Immigration Office to submit a TM.30, provided that you bring a copy of the house registration book, the owner’s identification card, and the rental agreement.
Once your wife has obtained her house registration book and you reside at the property, you may jointly register a TM.30 for yourself. This procedure may also be completed electronically.
You may still apply for a six-month multiple-entry tourist visa prior to departure. This gives you up to nine months. I assume that she also meets the requirements for the 60-day visa exemption. In this case, it is recommended to begin with that option and contact a licensed transport company to inquire about the practical duration for continuing border runs in order to obtain new visa exemptions. At the same time, you could explore the possibility of applying for a DTV from a neighboring country, provided that the relevant eligibility criteria can be met.
Subsequently, you may in the end apply for a Non-O visa within Thailand, supported by an income certification issued by your embassy, provided that you meet the minimum monthly income requirement. Should this not be the case, you will need to submit your application outside of Thailand in order to be eligible to open a Thai bank account.
Health insurance is important, but it’s clearly an advantage to be able to choose the insurance you prefer, rather than being tied to a Thai health insurance policy approved by Immigration for the rest of your time in Thailand. That’s why most people opt for a regular Non O visa as the basis for a long-term stay in Thailand. There’s really nothing to gain from choosing a Non O-A visa when you plan to apply for an extension of stay in Thailand. In fact, you’re only making things more complicated for yourself, as you’ll also need to obtain both a medical certificate and a police clearance.