The initial Non-O from outsude or inside Thailand and subsequent extensions do not have an insurance requirements. The Non-OA from your home country and the subsequent extensions both do.
a new extension is not granted on the day the previous stamp expires if, for example , it is applied for 30 or 45 days before expiry, it is applied to the existing stamp date and can be inked in as soon as the 2 or 3 week under consideration is completed (if there is an under consideration period)
Easier I'd say for you to get the 12 month extension plus re-entry permit rather than apply for a New Non-O. One thing to consider is when do you prefer your 12 months extension to occur, the same month each year that your current Non-O expires or the month that your new Non-O will expire when you return?
1 added to your current exit date, 2 you'll need to buy a new re-entry permit and 3 you need to be in the country to get your new extension inked in, go out beyond your current exit date without your extension you start again