One of the qualifications for an Extension of Stay based on marriage is a history of 12 consecutive months of qualifying wages in Thailand not what will happen in subsequent months so I don't accept what you were told
No need to "forget about it" as the 800k is needed for just over 5 months for the first extension of a Non-O obtained from outside Thailand then nver fall below 400k for the duration of the first 12 month extension while transferring 65k a month in international transfers for at least 12 months to apply for the second and subsequent 12 month extensions.