I am doing the same thing, I entered on 45 days, 28th March UK Male, Married for 11 years, Thai bank account 400k plus.
I am being dealt with by Yasothon immigration, a very helpful team there was informed, by them that.
1. towards end of 45 day entry apply 30 day extension, which I have done.
2 apply for 60 day extension, on day of expiry of 30 day, or as near to that date, if falls on weekend, holiday, which for me is next Saturday so will apply next Friday for 60 day extension. As the 60 day will start the day you apply so I will lose one day unlike the initial 30 day which you can get before and will run from day your initial stay expires.
3. two weeks prior to end of 60 day extension then apply for 90 day Non O visa, and then can hopefully do extension of stay based on marriage.
was told to bring original marriage cert and KOR 2 all of which I have, and also the standard passport wife ID ect.
please note I am registered TM30 with immigration when I arrived.