31 and starting over

I haven't seen a lot of post on here that were similar to my experience so I am reaching out. I am 31 years old with a husband of 12 years. We have two boys that are 9 and 11. I have always wanted more but it took my husband a while to get on board. We are trying for our 3rd and final baby! I am so excited to start this journey but I am also extremely nervous because my kids are already so grown up. My husband and I have always had a strong marriage but it is better than ever right now. He is really nervous about what it will do to our family structure. I just know it will be amazing!  I have always wanted a little girl but I am afraid to let myself hope because a healthy a baby is all I would ever dream of asking for. I was so young when I had my boys that I feel like this is my chance to really enjoy the experience. I don't want to be without kids in my home at 40 years old. Being a mom is my favorite thing about life. Has anyone else gone through this and how did it affect your family/marriage? Were the older kids happy about it?