Hans, between what James and Benjamin have advised you have your solution. As you have no ties here in Thailand you may wish to travel. On a tourist visa is the easiest way forward for you to stay here. If you decide to stay here on a OA visa and extension you have other issues with which immigration office you use for reporting and being approved extensions of stay. Come here first and see how it fits with you. Take the advice. - Get the Tourist Visa and whatever is required for your intended length of holiday. The Thai embassy in your country will tell you exactly what you need before they issue a tourist visa, and is hands-down the easiest way for you.
Go see a lawyer in the province where you live, is the best advice. In any event you will need a new visa. You may qualify for retirement visa but will need the monthly income or seasoned 800K. I suggest the will option is better. As well as the notation on title that you can live there until you die (May offer protection from being kicked out by family if your wife is incapacitated). Perhaps even have it written that upon her passing first, the property is to be sold upon the terms acceptable to you, and with you as the beneficiary.
, My personal assistant is Thai. She said she read on one of the Thai news ...But have just asked and she has said Noooo! They close now to 31st....So to clarify the distinction. Post Offices closed until month end...I now doubt as would have been BIG news by now. Maybe her source is a friend of an associate of the daughter of the service station attendant's brother who is always right, and overheard by mistake a chat between post office workers.....😂
So I assume you already in Chieng Rai, and havyour wife has filed TM30 within 24 hours arriving at your wife house. Chiang Rai office when I was there a few years ago don't get many farung so you may be fast-tracked, as not many officers English knowledge.