you were misinformed at the immigration office, it's not complicated for a 'married to Thai national' yearly extension, money is 400,000 in the bank account in your name only for 2 months prior to the application TM7, cost 1,900thb
you will need a non-immigrant visa to apply for the yearly extension, visa exempt can be converted within Thailand cost 2,000thb
if you were married in Thailand, there is less jumping through hoops than if you were married outside Thailand
a 'retirement' yearly extension is easier but the money is tied up in your bank, 800,000thb for 6 months dropping to 4000thb for the remainder of the year, topped back up to 800,000thb 2 month prior to date of application for the subsequent yearly extension.