we had 3 dogs when we first started TTC DS, one was from the pound, and was a good dog but couldnt trust him as much as the other two. we said we were thinking of maybe finding somewhere else for him and a week later my friends mum wanted him. if the good situation didnt turn up i dont think we would have actually got rid of him, but i think it was meant to happen. he is very happy there and we saw him once or twice after that.
we got a cat when ds was a couple of months old,to have an animal inside, and other than closing his door overnight so she doesnt go in there (only because we had never had a cat before so thought it was best) they are very good together.
Just do what you want, thinking it through like you are shows you are clever enough to not let silly things happen.pets are kids too, so why would you have to get rid of one to have another??