Can I apply for a Thai Non-O visa for caring for my half-Thai child without my ex-girlfriend's signature?

I have a dependancy Visa based on a non o visa but you must have sole custody to be granted this

I live and applied it in Phuket

On the last years I did it alone but before they always requested the signature of my son’s Mather in front of them

You need to first apply for the 90 day Non-O visa based on being the parent of a half thai child and that requires you show 400K baht in a thai bank account in your name only transferred in from overseas OR a letter from your embassy stating you get 40K baht a month in income OR legally working here and getting paid a salary of 40K baht a month.

Go to your immigration office and get the hand out that lists the requirements as far as the documents you need to apply for the 90 day Non-O visa based on taking care of your half thai child. You do that, get the 90 day visa then when that runs down you apply for the yearly extension.

You WILL need the document from family court that grants you legal parental rights for sure, BUT again go to the immigration office you use to get the list of requirements