Hi D.,
I can very much relate to how you are feeling. I felt the same way several years ago. At the time my children were
10yrs. and 7yrs. 1 boy, 1 girl, but I still wanted another one deep down. My husband did not agree with me at the time and it made me sad to think my daughter would never be a big sister. I was almost 35yrs. old at the time, my husband 39yrs. After several more conversations about having another child my husband agreed to try. I became pregnant right away, on my husband birthday, what a gift!! I am so happy we had a third child, a boy! He looks just like my husband, the kids just love having him around (most of the time)! They are 13yr. and 10yrs. now, and the baby is almost 2yrs. old. It's great having older children, they help out and I think it's been a great experience for my older son, my daughter is another mother to him. I say go for it if it's what you both want. Your lives won't change that much and you will enjoy the experience all over again and for me I think I enjoyed it so much more the third time around.
Good luck and take care,
V.