Kim Kardashian's theory on her pregnancy is quite simple: "Happy mommy, happy baby," she told Lara Spencer on Good Morning America today.

It came as quite a shock when Kardashian, who is notorious for sky high designer heels, tweeted Monday, "I never thought I would ever say this… But I'm wearing flats today," which begged the question of how she is handling her wardrobe decisions throughout her first pregnancy.

"You know what, they actually hurt my back," Kardashian told Spencer of her flat shoes. "I love high heels … Whatever makes me feel good, I want to wear. And I love wearing heels. I'm trying the flats, but we'll see."

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Kardashian also revealed a bit of advice her older sister, Kourtney, who has two children, offered her about the downfalls of being pregnant while in the limelight.

"Kourtney warned me when you become a mom and become pregnant, there will be this whole new group of critics that will criticize me for everything you do," Kardashian said. "If I wear one color clothes, I'm in this kind of mood. Or if I wear heels, they're harmful."

But Kardashian has managed her growing belly with ease thus far, assuring Spencer, "I feel really good. I have so much energy. I'm not tired. I haven't had morning sickness. I feel really lucky about that."

Her good health and positive attitude bodes well for the reality star turned film actress as she makes appearances to promote the new Tyler Perry film, "Temptation," she's starring in alongside Vanessa Williams. In the film, which opens March 29, Kardashian plays Ava, assistant to millionaire matchmaker Janice, who is played by Williams. The film tells the story of a young, married woman who is tempted into betraying her husband and suffers huge consequences because of it.

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Kardashian said getting involved with the film was "really fun" and "really different than shooting the reality show" at home with the rest of her Kardashian clan.

"I found I was definitely comfortable in front of the cameras because I'm so used to it at home when we're filming, but it's almost this pressure because there's so many people depending on you for the script and you want to make sure you get everything so right," said Kardashian. "It was fun though. I want to do more."

Kardashian also added she enjoyed playing the role of "a mean girl," something she confesses her sisters do not let her get away with at home.

"My sisters put me in check, but it was fun to play a character," she said.