@Mike ********
Just a thought. If you're age 50 or over you could get a retirement extension rather than a marriage extension. Especially as you seem to be bringing over 800,000 baht which is the requirement for retirement, marriage only requires 400,000 baht.
In general, a retirement extension is easier, more convenient to get than a marriage extension. You only need documents from your bank proving you meet the 800,000 baht balance in a Thai bank. You need other evidence for a marriage. You get the retirement extension approved immediately. You get the marriage extension approved after being under consideration for a month. You may get a home visit for the marriage extension but not for the retirement.
The only real advantage for the marriage over the retirement extension is less money needs to be kept in the bank for marriage than retirement. And you can withdraw that money to use outside of the mandatory balance period (2 months before application and 1 month after until you receive final approval), where as for retirement it must be 800,000 baht 2 months before application and 3 months after and then for the rest of the year never below 400,000.