Can I Convert My Non B Visa to a Non O Marriage Visa After Stopping Work?

Wouldn't it be a lot simpler to change the reason for your extension of stay to marriage now (assuming your funds are seasoned) then come march all you need to do is cancel your work permit. No need for a new visa, no need to leave the country.

Then you should be able to simply change the reason for your extension from working to married without any need to obtain a fresh visa. The work permit you'll need to cancel.

Who were you responding to?

To originally receive the Non B, you needed documentation from employer it was issued by an Embassy/Consulate outside of Thailand and was valid for initial "entry" into Thailand. Upon entry, Immigration gave you a permission to stay of 90 days, which they give for the majority of Non-Immigrant Visas regardless of category (B, O, etc.). To remain in Thailand, you would have applied for an extension of that stay at Thai Immigration for the purpose of teaching (work), which also required a Work Permit. The extensions could be renewed for that purpose so long as you continued to work and hold a work permit. The Immigration Rules for granting an extension of stay based on marriage requires you entered on a Non Immigrant Visa - it can be "O" or a "B" or some other category. I would suggest you check with your local Immigration Office to see if they will accept it for a marriage extension without the need for changing your Visa category.