A source close to the Spears family tells TMZ ... Jamie's not sweating what Britney has to say about him in her new book, "The Woman In Me," because she's already trashed him both in court and on social media, once saying she hoped he'd spend the rest of his life in jail.

In addition to Britney's book ... his ex-wife, Lynne, and Britney's younger sister, Jamie Lynn, both released memoirs detailing how Jamie was an absent father during Britney's upbringing ... which coincided with his struggles with alcohol. In other words, they've all pretty much said everything, so what else is there to know?

Fact is ... Jamie's already taken ownership of being a bad dad when Britney grew up, but when she was in dire straits back in 2008, Jamie came to L.A. to help her and stayed for the next 13 years as her conservator.

Britney's lawyer, Matt Rosengart, has alleged Jamie fleeced her for millions of dollars during that conservatorship, and Britney might be addressing that as well. But our sources say so far, Rosengart has not gotten a single penny from Jamie, in part because almost all the expenditures were court-approved.

Short story ... we're told Jamie has no clue what made the final cut in Britney's memoir ... and he's not interested in finding out because he lived through it and knows the truth.