I love using The Free Dictionary to find words containing/beginning/ending with anything. They list results by letter count and have different databases of results so you can filter by crossword acceptable/scrabble/all. As for the multi-word ones, I use the google search bar! Taking a word like RIDE and typing in "RIDE A" to see what suggested autofills appear—that's how I found RIDEALONGS. There's probably better resources out there but this is my workflow for now
I'm also currently reading Pride and Prejudice, but didn't even realize it worked with this theme until halfway through my planning! Funny how things work out