We are the same. I dont want another child for many reasons but one is just that we are so happy as we are. We never wanted more than one.
I think that when people say it is selfish to only have one child they are making a big assumption that children with siblings are better off than only children. I don't agree with that assumption and I think it has to be a case by case situation. All children need to get one on one time with their parents, all children need to be given a wide range of experiences, and all children need to have lots of time to socialise with other children of all ages (not just siblings). I think you can provide well for one or more children with commitment to their needs.