This has only just been introduced recently, The covid Insurance requirement is self explanatory, however you also

need general Insurance from a Thai Company.......

 

• A certificate of health insurance issued by Thai insurance companies covering the entire period of stay in Thailand containing the detail of coverage as follows; In-house patients of not less than THB 400,000/policy year, as for out-patients, not less than THB 40,000/policy year. More information can be found on https://longstay.tgia.org/
• A photo of medical insurance policy (in English) which expressly covers treatment and medical expenses in relation to COVID-19, with minimum coverage of 100,000 USD. The insurance must cover the total duration of stay in Thailand.

If you follow the link, or make subsequent enquiries to Insurance companies, they all seem to think that you need Insurance for a NON-OA, which is not the case as you only need it for 3 months, appears to be a grey area, Non-O has been available from other countries for some time, was general Insurance a requirement or is this a new addition?, or are you required to take out 12 month Insurance for a 3 month duration of stay?

You will need the insurance to get the visa. Ninety days is enough. If I recall some people using travel insurance to meet the requirements. They may not show the outpatient/inpatient coverage separately but it will cover all treatment up to an amount higher than the 400k baht minimum.

The 40/400k baht insurance is shown on about all embassies and official consulates since it was offered at those that do not the non-o for retirement.

Another option is to enter visa exempt or with a tourist visa and apply for the non-o visa at immigration.

 

OP, skip the non O based on retirement. 

Enter Thailand visa exempt and obtain non O in Thailand.

One thing to be aware of is that you will require a Thai bank account with 800k on day of application.

Not a big deal if your intention is to obtain 12 month extension.

Using an agent for bank account would speed that up and make it simple.

Be aware that the visa exempt 30 days can be extended by 30 days..

1900baht.