Your wife just had a baby. Your first baby. Now is not the time. She is going to need you to support her physically and emotionally for awhile while the dust settles.
I've already had a poly V relationship and I am currently in my eighth month of pregnancy. I miss having a female partner around as I was the one who was at the center of the V. But...my husband brought up going to poly events, seeking out a female partner, and even exploring some of the swinger clubs as soon as the baby was born. Even half considering it, I started crying. I honestly just can't imagine all that while adapting to a second child! And I felt like my husband wanted me to have a second relationship to take some of the pressure of support off of him. Pregnant women/new mothers are not rational. And now is not the time to bring up YOUR needs. My husband wants me to find a second relationship and it upset me enough. If HE wanted another woman in the near future I think I'd kill him for even suggesting it. And, as I said, we've ALREADY accepted our relationship as poly.
I'd rather be hated for who I am than loved for who I am not.