The only film version that really comes close to the novel (that I've seen) is Kenneth Branagh's early 90s take; it's flawed, but worth seeing.
There's an old Swedish production called Terror of Frankenstein
that's the most faithful one I've seen. It's probably faithful enough to be shown to a class studying the novel.
It's a decent little movie, but if you check it out, be warned that it's very dry. I'm glad to have it, but it illustrates why adaptations of the novel tend to spice it up a bit.