StAG 5 - Do I qualify, and what documentation is required in my circumstances?

Hi, I’m looking to see if I satisfy the requirements for German citizenship by descent through my grandmother. I am putting together a list of documentation that I need for my application.

Background:

My Grandmother was born in 1942 in Germany. She moved to the UK and married my English grandfather in January 1964. My mother was born in December 1964. My mother did not automatically gain citizenship due to discriminatory practices, which meant that before 1975, only German fathers could pass on citizenship by descent. I believe that my grandmother did get citizenship in the UK, but this wouldn't have been until after my mother was born.

Current Documentation:

Me: Passport (UK and Australian), AUS citizenship certificate, UK Birth Certificate, Police background check,

Mother: Birth Certificate, Passport, Marriage Certificate

Grandmother: German Passport, Marriage certificate, birth certificate (possibly), trying to get hold of UK certificate of naturalisation (is this necessary?)

Great Grandparents: What documentation do I need here? I am really struggling to trace my German ancestry. I know the names of my grandparents. I know where they lived in Germany (Alsdorf, Aachen), the date and the location in Germany where they were married.

I have read of people providing birth certificates and other documentation of great-great-grandparents. I don't have any birth or marriage certificates. If these are required, how best do I go about getting hold of these?

Many thanks,

M