I assume you are applying for a non-o visa based upon retirement at a embassy or consulate.
That may because the non-oa visa now requires $100,000 or 3 million baht of coverage.
You should be able to find insurance in the amount for the non-o visa. Requirements follow.
"2.6 Applicant must be medically insured for the entire period of stay in Thailand with the following coverage:– Outpatient benefit with a sum insured of not less than 40,000 THB, and– Inpatient benefit with a sum insured of not less than 400,000 THB"
Edit: You could apply for a non-o visa at immigration after entering with a tourist visa or visa exempt that does not require any insurance.