3 months
Ok, I think your best option is to make new 1 year non immigrant visa '0'/marriage.
It can be done in your country without the need to show money/income.
But you didn't really gave us enough details that we can help you....
For how long do you want to stay in Thailand?
Do you want an extention of 3-6 months? 1 year?
+ More information.
Can I Get A New Non-Immigrant "O" Visa While In Thailand?From Police order 777/25512.18 In the case of a family member of a Thai(applicable only to parents, spouse, child, adopted child or child of his/her spouse):
Permission will be granted for a period of not more than 1 year at a time.
(1) The alien has obtained a temporary visa (NON-IM)
(2) Proof of family relationship
(3) In the case of a spouse, the marital relationship shall be dejure (legitimate) and de facto;
(4) In the case of a child, adopted child or child of his/her spouse, the said person must not be married, must be living with the family, and must be less than 20 years of age; or
(5) In the case of a parent, one of parents must have an average annual income of not less than 40,000 baht per month or a money deposit of not less than 400,000 baht for expenses within a year.
(6) In case of marriage with a Thai lady, the husband who is an alien must have an average annual income of not less than 40,000 baht per month or a money deposit in a local Thai bank of not less than 400,000 baht for the past 2 months for expenses within a year.
Note: Two months first extension after that 3 months
Documents needed:
1. Application form T.M. 7 with one photograph size 4x6 cm. and Visa Fee 1900.-Baht
2. Copy Marriage Certificate
3. Copy Kor Ror 2 from amphur office (not older than six months)
4. Child's birth certificate (if any)
5. Copy wife’s house registration
6. Copy wife’s identity card
7. Copy passport, non-Im visa, arrival card.
8. Interview the husband and wife for confirming status of husband and wife
9. Map to residency
10. Picture of house and family, in house and outside showing house number.
With money in bank option.
1. Letter from bank same day or day before stating bank records, make a transaction just before to get it up to date.
2. Bank account must be in Husbands name, joint accounts will not qualify.
With Income option
1. A copy of work permit
2. Personal Corporation income Tax (PND.1) in latest 3 months and personal income tax for previous year with receipt
If not in Bangkok, all of the above in two copies