Defoe's work was written some time after the plague, and Defoe would have only been five years old in 1665, and the work is regarded as an historical novel in current parlance. However, Defoe went to some great lengths and detail to bring the impact of the plague home to the reader.
Samuel Pepys' Diary is a more contemporary writing, although I have (admittedly) not read it in its entirety.
Pepys’ diary is fascinating! I’m lucky to have the complete set which I picked up in a 2nd hand bookshop. Even a edited version is great reading.
It is a misconception that “common grave” denotes mass burial. It is more accurately a “Commoner’s grave”, generally one in non-consecrated ground on land provided by the cemetary owner and not the family. It may contain the remains of several unrelated people who died about the same time, but doesn’t really fit the image of a trench filled with bodies, i.e. a mass burial.