Jennifer Aniston can't wait to wed! This week's issue of PEOPLE goes inside the "small affair" she's planning for their special day. There's the man: screenwriter-actor Justin Theroux, 41. There's that engagement ring. There's a slate of films and new beauty ventures, renovating a $21 million L.A. estate in hopes of soon "normalizing and nesting," as Aniston recently told PEOPLE, and yes, planning a wedding. With her film, based on an Elmore Leonard novel, set to wrap in Connecticut on March 8, "Jen and Justin have a date" set for soon after, says a source close to the actress, noting that the twosome have designed their wedding bands and Aniston has a dress in mind.

"It will be a small affair with their closest friends," says the source. Likely among them: Aniston BFFs Courteney Cox, Chelsea Handler and Mandy Ingber, all of whom headed to New York to celebrate the actress's 44th birthday at the Greenwich Hotel on Feb. 11. The bride-to-be "is crazy about Justin and can't wait to be his wife," says the source. "She plans on privately changing her name to Theroux. She likes the way it sounds and jokes that [Jennifer Theroux] sounds very posh."

Aniston has found an ideal partner in Theroux; one who shares her passion for hard work and penchant for being a (very well-toned) homebody. "They both have the same work ethic and love to bounce ideas off each other," says the source. "Jen seems more confident than ever, and they've become a great team." Their partnership was on full display at the Oscars, where Theroux kept a supportive hand on Aniston's back throughout the red carpet gauntlet and held court by her side at the Vanity Fair bash. "They really seem to have perfect chemistry, like they complete each other," says a fellow party guest. "There's a perfect balance. He was doting when she turned to him, but the overall vibe was simply fun and effortless."

Aniston has also adopted a very Zen approach to their future together – including any plans to start a family. "Jen never thought that kids automatically mean a happy life," adds the source. "She's always said that she would love to have a baby, especially since Justin came into her life, but she won't be upset or disappointed if it doesn't happen. She loves life with Justin as it is." Yet the actress, who says she's gained a little weight because of a knee injury, is "comfortable in her own skin and doesn't feel a constant pressure to be perfect," says the source. "And Justin has always made it clear that he loves her just the way she is."

At home with Theroux and their two "babies," dogs Dolly and Sophie, Aniston "feels like she is at a high point," says the source. What advice would she have given herself 10 years ago? "I would just say, 'You're doing exactly what you're supposed to be doing,'" the actress recently told PEOPLE. Before Theroux, "Jen was always very grateful for everything that she had. But now life could not be better," adds the source. "And she deserves all the happiness in the world."

The new issue of People magazine is at newsstands everywhere now.

*Also In This Week's 'People'*
What Does Princess Kate Read? "She Came In Looking For Philippa Gregory Books"
Benjamin Bratt: "I Really Enjoy [The Voice]"
Phillip Phillips On Jonny Lang: "If I Could Have Anybody's Voice, It Would Be His"
'People' Special Report On Gun Violence – There Is No Safe Haven