this is not recommended as even agencies are struggling to open bank accounts this year on a tourist visa, so the price has increased. Much easier to get the non-O before coming to Thailand.
If not, why do you want to see an immigration officer as that is going to be the first thing you need. You can get a list of your local immigration office requirements to apply for the non-O without making an appointment, just ask at the front desk.
You need to apply for a non-O based on being over 50 online (not a tourist visa). When you get to Thailand after opening a bank account and depositing 800,000 baht for 2 months, you can apply to extend your stay for 12 months (this is not a Visa, you use the visa to enter Thailand initially). I don't know how long it typically takes at your Thai Embassy, but I think there are two in the USA, so it might be a good idea to state which one you are using to get better replies. Good luck.
I feel your pain and have faced similar situations not at immigration, but at various Amphur. Silly question but are you over 50 and have you considered applying for the non-O based on retirement instead, as it's very simple. I have chosen to not go down the marriage visa route because of the challenges you are encountering!
you need the original divorce paper, but you can get the freedom to marry document from the UK Embassy in Bangkok. Make an appointment online. You then need to get it translated.