@Mark *******
If you want to continue with OA Visa just keep applying at local immigration office every year, you will need the 800,000 baht in your Thai bank account 3 months prior.
If you want to change to the Non O Visa after the second year of Non OA just leave Thailand without a re-entry permit and enter Thailand again for a 30 day visa exempt in which time you can apply for the Non O, you will still need the money in your bank but not health insurance.