You are in luck. The Berlin embassy is one of the more straightforward ones when it comes to the DTV. Meaning, they don’t make unreasonable demands and pretty much only ask exactly what is mentioned in the law pertaining the DTV visa. What you would need is to show the equivalent of at least 500k THB / so about
*****
EUR in savings in a bank account in your name. In addition to that you need to show that you are eligible and allowed to work remotely. In my case I just showed them my German company registration. Bundle all supporting documents in a single PDF and add a cover letter explaining how you are free to work remotely from Thailand and that you have no intention of working for Thai customers. And you should be good.