Jessica Simpson on Raising Confident Daughters and Facing Her Own Body Insecurities (Exclusive)

The paperback edition of the singer's memoir features a new introduction and journal entries.

Jessica Simpson is taking lessons from her younger self. The 40-year-old singer tells ET's Rachel Smith how including past journal entries in the paperback edition of her memoir, Open Book, allowed her to gain perspective on some challenging times in her life.

"Whether I was mad at myself in a moment, whether I was heartbroken, whether I was confused, I just think owning all of those emotions on paper and confronting them is so important," Simpson says, adding that she decided nothing was "too intimate" to be published, as she included entries on her divorce, body insecurities and more. 

The act of handwriting the journals, Simpson says, allowed her to hold herself "accountable."

"My only competition is with myself, and that is actually the toughest competitor," she says. "... We have this life, right? So you might as well live every day as good as you can."

"I don't get an A plus in this. It is definitely something that I am learning along the way," she admits, "but it is awesome to go backwards in my life and learn from that little girl... I just appreciate myself so much more."

One entry that Simpson included focused on her body insecurities, which has plagued her since her teenage years.

"I can label it as insecurity, [but] that doesn't mean that it takes that away. That doesn't mean that I'm all of a sudden cured of insecurity," she says. "When I was going through it, I had the weight of the world on me and that's heavy."

That weight has lessened as she's grown up, though, and now Simpson is focused on how she feels rather than what the number on a scale reads.

"I have to rid myself of measuring up to what weight I should be because I've had so many people tell me what weight I need to be. I think it's really about how you feel," she says. "But if you're in the process, it's about sticking with it. It doesn't happen overnight. You have to be patient with yourself, you have to be kind to yourself, you have to love yourself, flaws and all."

That's a lesson Simpson wants to teach her three kids with husband Eric Johnson, specifically her daughters --  Maxwell, 8, and Birdie, 2. The couple also shares a 7-year-old son, Ace.

"They’re very secure so far. My oldest daughter is so much like my sister," Simpson says, referring to her younger sister, Ashlee Simpson. "The part of my sister that I've always envied is she is just unapologetically authentic and will take a risk -- with fashion or with beauty or whatever-- and then it'll become a trend and I'll end up hopping on the bandwagon. It's pretty awesome."

"I love raising somebody like my sister," Simpson gushes of Maxwell. "... I just need to be cool enough for my daughter and my sister." 

As for Birdie, Simpson notes that the tot "is the most independent of everyone in this family," before explaining why her youngest is the last child she plans to have.

"Oh lord, no. That's done... That was the last pregnancy my little body could endure. She was almost 11 pounds, so that was a hard pregnancy for me. It was a lot and three kids is a lot," she says. "I want to give them all that I have and be a working mom too, I just can't even imagine."

On top of her family life, Simpson, through Amazon Studios, has an unscripted and a scripted series in the works, both of which will be based off of Open Book and have its author as an executive producer.

"I have 10 years of footage. I've been doing that for a long time, just filming on and off -- big moments in my life, hard moments -- just feeling like there was gonna be a moment when I would use it... Now it's all come together in a very beautiful way and it happened throughout quarantine," Simpson says. "... It's gonna be very powerful, the doc series. Lots of moments that you won't expect. You'll have definitely moments where you laugh, too, but it's life."

As for the scripted series, on which Simpson is excited to "add characters and play with it," no one has been cast to play her just yet, but Simpson thinks "there has to be an unknown" actress in the part.

With all of her projects in the works, Simpson is incredibly grateful for all that Open Book has given her since its release last February.

"When I was writing the memoir, it was really me compiling a lot of my journals from my past," she says. "I was going through a time in my life where I gave up alcohol. I wanted to just journey back to the person that I was before that, and discover parts that I miss, and parts that I was trying to put a Band-Aid on."

"If we admit to it and own it, I feel like it makes life, and choices, and everything so much easier," Simpson continues. "... I feel like now, since the memoir has been out, I have never felt more of myself. It gave me permission to be who I am."

Open Book, Simpson's New York Times bestselling memoir, is now available in paperback.