Unless you are trying to avoid the insurance requirement you don’t need to switch to a non-O. You can renew your insurance and extend the OA for 1 year inside Thailand.
I was able to get my insurance company to coordinate my policy dates with my visa dates. Instead of trying to get a few days of insurance you should be able to buy 1 year + a few days.
This is one of those things where even if you don’t know the answer you can do with almost no effort and cost. Just do it. Bring it with you. If they ask for it then you have it. If they don’t ask for it they you aren’t out anything.
For a work permit, yes you have to change from the OA. You will have to work and pay taxes for 3 years to get citizenship. There is a Facebook group dedicated to getting citizenship. Hardly anyone does this but it is up to you.
I had an OA in Bangkok for 5 years as retired. If you are at the end of the first year of your OA then I believe that your first 1 year extension has to be the same as your original OA and that means you have to extend as retired for the first extension. The TM7 form for a 1 year extension has an entry at the bottom to enter the reason for the extension. This is where you enter "retired". I think for the second 1 year extension you can enter "marriage" on your OA visa. I also believe that even if you are on an OA visa, if you extend as married, you no longer need to have the required health insurance. Contact Tod Daniels about this.
If you don't want to go another year as retired then you will have to leave and re-enter to start the process for an O visa and subsequent 1 year extension.
Also, just because you got married it doesn't mean you have to extend as married. I continued to extend as retired after I married because the process and documentation is easier. You do have to meet the higher financial requirement for retirees though.