If you are in Vietnam, go to HCMC and apply for a 1-year multiple entry Non-O visa based on marriage to a Thai national.
This type of visa is valid for 1 year to enter Thailand. You are stamped into Thailand for 90 days for each entry until the last day. You need to leave and come back to Thailand every 90 days, but you can live in Thailand on it nearly 15 months.
Check Consulate website
Vietnam RTCG
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