You might want to visit this site which has a database of birch bark documents found in Novgorod area (10th-14th centuries). The Novgorod language is pretty close to both Russian and Ukrainian, and it is very different from Church Slavonic, which I heard was an artificial language developed solely for the purposes of Orthodox Church. Also the Novgorod dialect seems more natural sounding for a language to be spoken by people of various social classes. It is very interesting source of information about life in Russia back then, it's definitely worth a look.