When I was reading 'Wuthering Heights' for a class, I hit a wall around all the religious and class stuff that just isn't part of my modern frame of reference. The SparkNotes website was my lifeline, honestly. It breaks down the chapters with clear summaries, but more importantly, its 'Themes, Motifs & Symbols' and 'Analysis' sections are where the real gold is. They explain stuff like the significance of windows and the two houses in a way that clicked for me.
For more academic depth, I later found the website GradeSaver. Their study guide includes critical essays that dive into interpretations of Heathcliff as a Byronic hero or the novel's structure as a narrative frame. It's more formal than SparkNotes, but it helped me understand why professors love dissecting this book. I'd also poke around on Project Gutenberg. The text is free there, and sometimes you can find user-generated annotations or links to companion sites in the comments or metadata, though that's a bit more of a scavenger hunt.