I am the middle of five (and I don't suffer from middle-child syndrome, strangly). While as a kid, I always wanted to be an "only" as a teenager and now as an adult, I am SO THANKFUL for my siblings. I get along with all of them, we're very, very close - always hugging and saying "I love you". The thought of not having someone else who shares that type of bond with you (same parents, brothers, sisters, similar childhoods) is just unimaginable to me.
I have two kids (and we're done - although I do feel bad that my daughter will never have a sister and my son will never have a brother) I always tell them, "Some day, Mom and Dad won't be here but you'll be here for each other!" Although there are days I wonder what life would be like with one child, I see how they play together, how they kiss and hug each other goodnight and say, "I love you!" or how my son says to his sister, "If you're scared, I'll hold your hand." Nothing beats that and I wouldn't give it up for the more simple life with an "only."
I have a friend who was an "only" and she now has two daughters. She said that while she was younger, she liked being an "only" but now as an adult, realizes what she missed out on and that's why she had two kids.
Give it a year or so and then bring it up with your husband. Obviously, I think you BOTH need to be okay with another child, but maybe he'll have a different perspective in several months. Good luck in whatever you decide.