Can I extend my Non-O visa and stay in Thailand indefinitely through extensions and visa runs?

1 - you can indeed get a 60 day visit thai family extension without proof of funds with just your name on the birth certificate and documentation from the thai mother

unfortunately unless you have been granted legal parental rights by the decree from family court, OR your child is over 7 and you were able to get the parental rights granted at your local Amphur (City Hall) you can't get a year extension based on being the parent of a thai child. Even if your name is on the birth certificate, and/or your child has a passport from your country without the family court or amphur decree of granting legal parental rights you can't get a year extension

Samui was wrong and they were telling you the banked money method for a foreigner raising a foreign child (which is 500K baht banked for 30 days the first year and 3 months for every year after that). It is indeed 400K baht banked for the extension for raising a thai child, and at least officially there is no seasoning for the 400k, although more than a few offices want it seasoned the same as a marriage extension (2 months before the date you apply for the extension)

There is nothing stopping you from taking this 90 days, taking the 60 day extension and then going to a consulate to get a new 90 day single entry Non-O. They are issued at several consulates in the area. And you could get another 60 day extension on that too.

I know people who have done that for years and years (pre-covid shit show). The thai consulate in Savannakhet will issue that 90 day Non-O without proof of funds, but Vientiane wants you to show a bank account with 200K in it to get that visa issued. Dunno about the consulates in Malaysia.