It will just add to the happiness you already have. I am very glad I was blessed to have both sexes, because they bring different experiences to your parenting.
It won't be so different right away, but when he gets just a little older, you'll find yourself spending more time with pirates and dinosaurs and cars than you probably do now.
You are a very blessed mom, and I know that as you peek in on each of the three of them sleeping tonight, you know that God has given you some special treasures to care for.