If I understand what you are asking, then it is for the proof of accommodation, right? If so, then you just draft a very short letter stating that you "hereby invite [name] to come to stay at my apartment at XXX as long as you please." The Thai Embassies have templates for this also. A copy of your passport and your lease agreement/deed will be beneficial too.
You will need several documents from the bank. Unfortunately, I dont have a scan of those. And yes, Bangkok Bank might not know what you are asking until you show them. You can get a sample picture at the Immigration.
The 90-Day report you can do 2 weeks before and 1 week after the 90th day. If lucky the online system will work also for you for the next 90-Day report.