Records for Christburg (Dzierzgoń) and Marienwerder (Kwidzyn)

Dear All

I am travelling to Poland later this month to research my mother's Prussian roots - she was born in Marienwerder and grew up in Christburg. Any advice on where I might access records in these now Polish towns would be very much appreciated. The family names that I am researching are Kunz and Kowalkowski (later changed to Koll)