I follow this Vlogger "Buzzin Pattaya" on YouTube. He recently did a video on visa changes with a visa agent in Pattaya. I've personally never used this agent but apparently he is well liked in the local expat community. Recommend you give this video by Buzz a look see.
Go to the retirement desk at the Krabi immigration office and ask them. More than likely they have a preprinted list (in English) of what you will need for your extension. Then return on the day you plan to actually do your extension, with all of your affairs in order.
I wish you good luck. Getting your non-US spouse a green card to live with you in the US was challenging before the Dear Leader became POTUS on Jan 20th. I'd wager it's damn near impossible now.