How did you decide to have another baby?

Au
My husband and I are soul mates, he is my perfect match in every way. The only thing really missing is a baby of our own...I have baby fever horribly and I want to experience everything with him. We both have a daughter from previous marriages (they're 6 and 7), but we want another baby, a baby that is ours, but I just feel so torn. We've been out of the baby phase for a while, our girls are in school, we have our routine...
How did you know it was right to try for another baby?