Nice to hear from you again!
Unfortunately it's a common problem to find affordable flats or rooms in lots of German cities.
You probably already used the usual websites to search for ads, right? Like these ones:
If you are open to the idea of living in a shared flat (aka WG) you might find interesting results on one of these websites:
Just a little tip (that you might also already know): Back in the day when I searched for a room myself, I didn't just send a "copy&paste" mail to every ad that I was interested in. Instead I tried to give a brief self-portrayal that enabled the landlord/tenants to get a first impression of who I am.
In which city are you looking for a room? If you tell us we can do some research about organisations or initiatives that might be able to help you.
And what documents are you still missing?
I wish you all the best for your search. I know that it can be quite disencouraging sometimes, but you got to be persistent.