I got my Non O visa 4 years ago and did 4 yearly extensions bases on retirement. Without any problems. Easy process. I must admit i am lucky I can still use a validated income statement from my Embassy in Bangkok. So no mandatory money in a Thai Bank.
Go for a Non O. Much less demands to get it and to extend it. Extension in Thailand doen't need a mandatory insurance. In fact for me they are practicly the same. So go for the easy one. I see no benifit in taking a OA.