A minor other thing is that you will need to have an valid passport, valid at least as long as your new "Extension of Stay". I did totally forget that but while filling-out the application form for the "Extension of Stay" I suddenly realised that my passport would be invalid within 1 year.
So that means an extra trip to Bangkok to apply for an new passport. In the old days that was easy, just walk in and apply for it. And within a week you would have a new passport. Nowadays my embassy is not that easy anymore.
First of all I need to make an appoint via an external company. And I have to fill-out and print a application-form. And for a passport you need pass-photos that are correctly made according EU rules. Luckily there is shop making the guaranteed good photos opposite the embassy ... except the all building were that shop was is gone. Luckily on the parking compound of a condo next to it there is another (new) shop making the same photos. Of course not cheap.
Then just be on the right time at the embassy, ID yourself at the gate. Be checked, get a VISITOR tag and enter the embassy office. Well I must say the appointment system works well. No waiting, with efficient and friendly service. I was done within 10min.
Well and relieved of some money .... almost 5.000 THB for a new passport. Luckily it will be 10 years valid but if you travel a lot you might need a second (or new) passport within that time-frame.
And because you will need a letter to explain your new passport to the immigration, the embassy is so kind to supply that letter. Not free of charge of course ... mind you this your government .... a small token of almost 2.000 THB was taken.
So once I have my new passport the next step will be to apply for my new "Extension of Stay". I will keep you updated about that.
Update : It took a bit more as 3 weeks to get my new passport