The most important thing is that you both REALLY want another one. If you cannot convince your husband, you really should lay off. Men always feel overwhelmed with kids, they just aren't made up like us. One thing my mother always told me is, everyone's feelings are equal and she is right. As badly as you want to have a child, he equally does not. Children are such a fantastic blessing, you really do not want to risk your husband having resentment and that child feeling bad about him/herself.
Enjoy the blessings you have, you are so lucky you have them, you are so lucky you have the space, you are so lucky you have the money to give them everything to enrich their lives. Sometimes we just need to accept what we are given and are supposed to have, you just don't want to push it.
Now all that being said, if one day your husband caves and decides to go for it, you don't have to rush it and have a baby in the next year. There again, you are forcing nature, just let it be, life will go the way it is supposed to. I never wanted to have children and suprisingly had my first one just before I turned 30 and just had my 3rd one and turn 40 in 6 months. Like you, I could have a couple more and love it. I have enough energy, love and ambition to fulfill my life and my children's lives. Again, like you I sometimes feel I am missing a person, I feel like I am supposed to have one more. I have decided to stop though and count my blessings.
Good luck, you are a very blessed woman!