T.C.
It sounds like a lot for you guys to think about and talk over! I think it's good for you both to consider one another's feelings an desires and then in the end hopefully come to an agreement. I did want to share with you some of what we've been through since it sounds pretty similar.
Our first daughter was unknowingly born with a very rare fatal disease that causes aplastic anemia (bone marrow failure) and many different types of cancers, including leukemia. It's called Fanconi anemia (FA). It is a genetic disease and both my husband and I are carriers and both passed a FA gene on to her, which is the only way a child would be born with it (both of us have to pass it on). We have a one in four chance of having another one with FA.
Not only does she have FA, but she also has some physical abnormalities that are caused from FA (though not all children with FA have these). She needed open-heart surgery when she was born. She is hearing impaired, though can hear with hearing aids. She also had a cleft on her soft palate that was repaired (so only in her mouth). Plus some other physical issues. Her hearing/cleft issues have left her with communication problems. She is very intelligent and at normal levels for her age, but communication is quite a challenge. She has difficulty speaking clearly for others to understand, though she is making great progress. It has definitely been a challenge for her and has taken longer than usual for a child her age.
My point in sharing all of this with you is to also share that despite all of this, we felt very strongly that we should have another baby. My husband was more like your husband and was reluctant at first. I definitely didn't want to bully or force him into something like this because it needed to be a choice that he made and fully agreed with, especially if a second child ended up with FA. I didn't want him to blame me. But he ended up feeling very strongly that it was the right thing to do.
So when our daughter was four years old, baby number two was born. He does not have FA. We are SO thankful that we had our son. Both of our children bring us such joy and happiness and we couldn't imagine life without them. Sure FA is no fun, but we find more joy in our children than sadness in FA.
I am now pregnant with baby #3. It was a similar process. It always seems to start with me feeling like we should have another baby, telling my husband, then he thinks about it and tells me how he feels. With baby #2 it took a while for him to make a decision. With baby #3 it only took him a few days. I know some people think it's crazy to risk it, but all I can say is we know we are doing the right thing for us. (Plus, we are motivated by wanting a sibling-donor for a bone marrow transplant!).
Every family is different and the answer is different for each family. I totally support your desire to have another child and do not in any way think you are thinking of doing something ridiculous. I think your husband has valid concerns, and it sounds like you are considering those and being understanding to him. If you feel strongly that you should have another one, I do think it's important to express that to your husband and continue to talk about it until you come to an agreement/compromise. There is so much joy in seeing two of your own children love each other and have each other to be with. I totally encourage you guys to strongly consider having another one...but only the two of you know that is right for your family. If you believe in God that is a big thing that helped us decide what to do - lots of prayer.
I hope the best for your daughter. My little sister had a similar thing with her ankles, though less severe. She had to wear special little shoes that braced her ankles up. Good luck figuring out what to do!