Enigma, I understand completely. I don't think that choice is a selfish one at all. Like you, I can see many benefits from only having one child and just one from having more and that is because I think it might be nice for W to have a sibling.

DH is an only child and he doesn't feel as if he's missed out but every child is different and so is every family. It's hard in a situation like yours where one partner feels very differently about it to the other. I think that if you are honest with your DH about your feelings, you won't go wrong. He would surely understand that now wouldn't be the time to make any major decisions about increasing the size of your family if you are feeling uncertain.