Get the year extension then when you leave Thailand buy a re-entry permit so all you have to do is come back to Thailand before the 12 month extension is up.
This gives you the 3 months you want and another 9 months to re-enter to keep the extension alive.
I came to Thailand on November 6th on a TR60 visa using the old COE certificate.
They were both approved and I came on a one way flight.
It is as many people say though pot luck if the check in person for your airline wants to see a outbound/return flight. Just make sure you have a method of booking an onward flight there and then.
Ok thank you as I was planning on coming in on a 60 day Tourist Visa, extending by 30 days then applying for an extension based on retirement but if I have to get a non-O visa as a ‘bridging’ visa first so be it.