Honestly, the first title that popped into my head was 'This Side of Paradise'. Fitzgerald wrote it before Gatsby, and it's got that raw, youthful energy of the era, but it's more of a coming-of-age story about ambition and disillusionment at Princeton. It captures the mood before the parties really started. For the actual glitter and decay, maybe 'The Beautiful and Damned'. It's like watching the hangover in slow motion—a couple burning through money and potential, and it’s pretty bleak. It doesn’t have the mythic quality of Gatsby, but the social observation is sharp.
If you want the vibe from a different angle, I’d say try 'The Sun Also Rises'. It’s the Lost Generation in Paris, not Long Island, but that same sense of profound emptiness after the war, masked by drinking and frantic movement. The prose is so clean and devastating. Or, for a deep cut, 'Gentlemen Prefer Blondes' by Anita Loos. It’s a hilarious, satirical diary from a gold-digger’s perspective, and it’s surprisingly insightful about money, sex, and performance in the 20s. The movie adaptation is iconic, but the book is a witty, period-perfect gem.