I have a two room apartment for rent. Commission free. See
Apartment for rent in Frankfurt-SachsenhausenWe are moving out in August, and is available from 1st of September.
We rent from FAAG which CB has already linked. There are a couple of apartments available in our apartment block for immediate occupancy which are probably similar to our apt.
Our contract isn't fixed, we just had to give 3 months notice to quit. The notice is takes effect from the end of the current calendar month. Say you write the company/landlord with your 3 months notice on the 5th of May, the notice starts from the end of the May, so you are free then by the end of September. If you can get someone to take over during your notice period too, if 3 months is too long. But you'd be lucky.
You will probably have to install a kitchen or buy from a previous tenant. Apartments are really unfurnished. Not even light fittings included.