The new mom, who welcomed son Rennie David in February, called the flattering one-piece the "best" she's ever tried

Katharine McPhee's loving how her post-baby body feels in a swimsuit — especially one flattering suit designed by step-daughter Sara Foster!

One month after giving birth to son Rennie David, whom she welcomed in late February with husband David Foster, McPhee has been documenting her postpartum journey on social media, even sharing a filter-free look at her body in a tie-dye one-piece that Sara, 40, created in partnership with Summersalt.

McPhee, 37, snapped a mirror selfie from her bathroom as she modeled the flattering scoop-neck style swimsuit and shared the photo on her Instagram Story.

"Best one piece I've ever tried. Usually it's cut too low and the torso isn't long enough - straps are adjustable. So comfortable! You nail it @sarafoster," the star said.

katharine mcphee foster
Credit: Katharine McPhee Foster/Instagram

Earlier this week, McPhee posed in a one-shoulder, high-rise bikini and told fans she's been "loving" her curves since giving birth.

"Loving my curves because my baby gave them to me," the singer said as she took a mirror selfie.

Katherine mcphee
Katharine McPhee
| Credit: Katharine McPhee/ Instagram

Last month, McPhee told PEOPLE that she's in no rush to get back to her pre-baby body. "I thought I would have this pressure [to bounce back] but I've just been so grateful and happy that I've had a healthy baby and I've felt really good, emotionally and physically," she said.

"I'm so happy that I don't have this crazy pressure yet to fit into whatever jeans I have in my closet," McPhee continued. "I don't even think about them right now! In my everyday life, I would have an event coming up or need to work out and it's just really nice to have a break and be happy where I am."