So sorry for the late reply! I'm putting together my undergrad thesis on the Beach Boys right now and have quite a few suggestions.

Firstly, to get a sense of the first-person perspectives of the band, I'd take a look at I Am Brian Wilson and Good Vibrations: My Life as a Beach Boy by Brian Wilson and Mike Love, respectively. They do well to balance each other and provide different takes on the band's history.

To get a fuller grasp of the history of the band, I'd definitely check out Peter Ames Carlin's Catch a Wave: The Rise, Fall, and Redemption of the Beach Boys' Brian Wilson. It's a biography, but covers the entirety of the band's history from a highly readable angle. Keeping this in mind, it is prone to bits of exaggeration and is quite Brian-centered (being a biography) but is probably the best Beach Boys history on the market.

Charles Granata's Wouldn't It Be Nice: The Making of the Beach Boys' Pet Sounds and Dominic Priore's Smile: The Story of Brian Wilson's Lost Masterpiece are works on the makings of two of the band's most well-known musical projects.

If you want to get a bit deeper, and perhaps more academic, I have a few more choice picks. Long Promised Road: Carl Wilson, Soul of the Beach Boys is a solid take on the band from Carl's perspective, but works best when you already have some familiarity with the band's history. Kirk Curnutt's Brian Wilson is a fantastic character study, and does much to unpack the "Brian Wilson is a genius" myth. Good Vibrations: Brian Wilson and the Beach Boys in Critical Perspective, a collection of academic essays edited by Philip Lambert, is great, if far more inaccessible and a bit less readable than the other sources listed here.

Articles from their times also make good reading, just make sure to not accept their biases as fact, of course. Jules Siegel's iconic "Goodbye Surfing, Hello God" was written in the midst of the SMiLE era, and "A California Saga" and "The Healing of Brother Brian" are also great. I'd also check out this extensive fan archive: it's filled with good stuff, most notably hi-res scans of album liner notes and a rare copy of TeenSet magazine released by Capitol, the band's record label. This website also contains the booklets for the Beach Boys' release of The Pet Sounds Sessions.

Hope this helped, and feel free to reply or message for more suggestions!