Since you need some quickly, I'd read some Ursula K Le Guin short stories. She's very good at using an expansive vocab fluidly and organically without overdoing it. You don't want to necessarily overdo it, it ends up sounding bad. English has so many options to choose from that you need to sprinkle in more esoteric ones tastefully to avoid coming across as foolish, pretentious, or even being intentionally obfuscatory. Unless you're a university professor, then you get unique permission to use all the weird words you want.
Some of my favorites off the top of my head: obfuscate, vehemently, scintillating, lithe, poignant, behoves, loathsome.