To enter Thailand for three months, I believe a Non-Immigrant Non-O visa based on marriage would be best. From the consulate website at
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"Original Passport with a minimum validity of 6 months when entering Thailand
Duly Completed and Signed Visa Application Form (Download Visa Application Form) and 2 recent photos
Copy of the Applicant’s Passport
Flight Itinerary (DO NOT purchase your air ticket until your visa is approved.)
Hotel Reservation or invitation letter from the person who provides accommodation stating period of stay and full address of the accommodation. Signed copy of the accommodation provider’s identity card is also required.
Bank Statement or Proof of Income with a minimum balance of 550 Euro
For visit of Thai spouse or close family members:
Official Document showing relationship and identity card of the Thai spouse or family member
Residence Permit"
The cost is 70 Euros, and I believe one day turnaround time.