21 hours ago, ubonjoe said:

You will need a letter from your bank confirming your account and the balance on the day you appy. Example here: bank letter.pdf

Most office will accept the letter dated the day before you apply for the extension.

Your bank book will need to be updated on the day you apply to prove the 400k baht has to been the bank for 2 months  on the day you apply.

Here is my general list of required documents and etc is here. Marriage Extension Requirements 2.pdf

You can apply for the re-entry permit at immigration and at both airports in Bangkok on departure from the country.

 

You need to apply for the extension as soon as possible. You will get a under consideration stamp with a report back date on it that will be 30 days from the day you apply.

Think it might be worth pointing out that sometimes it can be longer than 30 days. My last 30 day under consideration period ended on a Friday, but when I turned up, Jomtien immigration told me to come back the following Tuesday afternoon.

21 hours ago, baneko said:

I currently don't have a flight ticket to return to work as they require a copy of a Covid PCR before they will purchase the ticket.

Presumably by "they" you mean your employers? If so, don't you have anything in writing from them in connection with your upcoming overseas stint which you could show to Sri Racha Immigration when applying for your marriage extension?

Should it be necessary, I have read of companies that sell just the flight bookings, just the booking not the flight. They are used apparently for who needs an itinerary for a visa. 

I've googled a couple of names, getitinerary.com and flightreservationforvisa.com. but  there are more. They seem inexpensive, maybe wise to keep in in your pocket and pull out in case of necessity. 

Good luck