Hi there-
I am an only child and for all purposes I was an only grandchild to my mothers' parents. I was "well loved". :)
Anyway, growing up as an only child had its difficult points but in general, I didn't really wish for a sibling until I was older. I had a lot of opportunities that had my parents had another child, I wouldn't have gotten and I did have to learn to be very resourceful and social as a result. While this was a good foundation, this is not what I wanted for my own family.
As an adult, I believe that the best gift you can give your child is a sibling. While they may not get along, to give them the gift of having someone else to share their life with is your gift to them. What they choose to do with it is up to them. That said, part of my decision had to do with the fact that my Dad isn't close to his siblings and neither is my Mother. So, once my dearest grandparents died, I was faced with the realization that once my parents die- it is just me and that would be a very difficult place for me to be...all by myself.
I have a 3 1/2 year old son and am having my second baby in 2 weeks. This decision was not easy for us to make in the sense that having my first was very difficult for us and caused 3 years of constant medical attention for both my son and I and put our family in a financially difficult situation. Having another one was equally difficult but has been (so far) easier than the first. That said, we faced a lot of criticism from family and friends about why we would put ourselves through this again. The answer really came down to the fact that I needed/ wanted to have a sibling for my son. In addition to all of this, both my husband and I are 4 hours from our hometown and we don't get a whole of visits from the family as a result. My parents come to visit regularly but his family is hands-off unless we go see them. So, this made it even more apparent to us that once my parents die, we are really alone...besides our friends and "family" that we have established here in IL.
Having said all of this, I think in the right situation having an only child is a good decision because you can give them many opportunities, attention, etc. that you can't do with two or more children. If you have a good support system and plenty of family in and around the area (and it sounds like you do), I think this is a good foundation for an only child to grow up in...especially if you have medical issues.
I think that no matter what your decision, it is your decision and you shouldn't let others influence you. I would urge you to do what is best for your family and taking into consideration your situation- financially, emotionally and physicially is the most important thing. Looking at your external resources- friends, family, etc. can also be very telling on what makes the best situation for your family. For us, the lack of family was instrutmental in our decision but it sounds like you have that in spades so do what is best for you and your hubby!
Good luck!