Try the Penguin Classics hardcovers. Frankenstein for example[0] includes an amazing abridged version based on the original manuscript and later revised editions as well as a very engaging historical account of the author's life, times, and influences when she wrote it. These are also important things to understand about a story as well and can give deeper insights into its inner structure.
[0]http://www.penguin.com/book/frankenstein-by-mary-shelley/978...