1. I recommend a good lawyer. Especially the knowledge which documents can substitute which documents in such cases, can really improve your chances of succeeding.
2. Since you have also polish ancestors you should consider getting the Polish citizenship. Since Poland is a member of the EU you have the most important rights in Germany as a Polish Citizen
3. If you really want to stay with your plan you should consider to take a look at parish registers (Kirchenbücher). Some of them were copied to microfilm and are available today.
4. A surprisingly large number of files has survived. You should at least write a letter to the city hall of the polish city and ask. However, especially in small cities you should write it in polish and expect to pay some few.