Take some of the so called experts comments with a pinch of salt. There's plenty of visa experts here on Sadbook that don't know what they are talking about.
Seems you don't know what your talking about. Applying for any visa doesn't mean your passport cannot expire before your visa does. I applied and got a Thai visa many years ago and my passport was due to expire before the visa expiration date, so I renewed my passport at the British Embassy in Bangkok, went to immigration armed with my old corner cut passport with my visa in hand. My new passport and immigration transferred my visa from old to new.
I have mates who are married to Thailand ladies who I used to work with and they all told me that to get a non-O based on marriage they only show 400k in their Thai bank account and similar when they go for the extension based on marriage they only have to show 400k in their Thai bank account. They have never had to show a monthly income to get their extension, or so they told me.
I didn't know you had to show a monthly income. I thought all you had to show to get the extension based on marriage to a Thai was a Thai bank account with at least 400k deposited.
Years ago you only needed to show 200,000 baht in a Thai bank account. A few issues with this monetary requirement that are anyone 50+ can apply for a non-O and a twelve month extension. So anyone who hasn't actually reached their countries official retirement age to receive their state pension could go to Thailand, have mates there that would lend them 200,000 baht, process a non-O and then the 12 month extension, then give the 200,000 back to whoever they'd borrowed it from and then what would they do to support themselves for the next twelve months. I reckon that is the reason they upped it to 800,000 THB. At the end of the day if you are in receipt of a state pension from your country and it can support you in Thailand, then there should be no reason for showing 800,000 THB in a Thai account. Just my opinion. By the way, I knew a Swedish guy who lived on the road from my village to Udon Thani. Nice guy with a Thai wife and daughter, but they didn't have much. They had a modest wooden home and next to the home a smallish pond where they farmed cat fish I presume. Now this guy had to borrow the then 200,000 from a friend every year to get his extension. Perfectly respectable chap unlike some of the dubious characters that are hanging out permanently in Thailand.