There is no such requirement of showing proof of a state pension for an METV. Most people are NOT retired who get it. You usually have to show a letter saying you are employed ( but since you are not, the embassy or consulate in your home country told you proof of pension was ok) and you need to show about the equivalent of $7000 USD and ticket out of Thailand and some accomodation here ( I just have shown a two week hotel reservation that I cancel because my plans change before I arrive). A few other things like a pic and application are required. Some consulates have different requirements so always check.
I also think you are NOT getting 90 days upon arrival with an METV. You are getting 60 days but you are extending that entry by 30 days and going to immigration and paying another 1,900 baht for extension.
So a lot of your information is wrong.