When To Add To Familys

Hello Everyone!

My name is Kimberly and I'm a single mom of a four year old. I have been with the love of my life for a year now and I know he is the one I want for the rest of my life. My daughter takes to him like no other but I wonder when is the right time to add another person well baby into the mix..... I fear the longer I wait the harder it is going to be for my daughter to transition I'm looking for advice maybe from someone who has been in my shoes