I did it back in March. On top of the updated passbook, bank statement, employment certificate, I also took all the documents that I used when I applied for the first time around. The IO was friendly but he also had me get a proof of legitimacy of the employment certificate. Basically he wanted a print of the email that had the certificate attached with the company’s email address visible. I had nothing to worry about since all my documents are legitimate. He also asked me to print out my portfolio, which was used when I applied but I thought I wouldn’t need it during extension. After that the process was all in their hands now. They appointed me to come back in a week time to collect my passport and do 90day report as soon as I get it. Everything went smoothly. Also, the queue wasn’t that long so I’m very happy about that.

If you own a Thai Bank account, they have an option to queue up for “Bank statement and certificate”. Very easy to get, they’ll just require a few signatures from you and they’ll get you both or either one of them as you requested