I don't think you should feel guilty for only having one child. I come from an extremly large family - I'm one of 11 - and none of my siblings has chosen to have more than 2 children, all late in life. My partner is an only child and I have never met anyone so secure, happy and self-contained. I put this down to an extremly good relationship with his parents.
Few people speak of the downside of large families. Although I get on very well with most of my siblings, given the chance we would have all chosen to have come from a smaller family. Quite apart from the lack of material posessions, which never really bothered me, it was the fact that parental attention was spread over so many more of us. I was lucky if I had a conversation with my mother once a week. Essentially we were left to get on with bringing up ourselves. I don't mean to say I had an unhappy childhood, but I am always envious of my friends who can relate to their parents as friends and equals, who can have an uninterrupted conversation with them, and who's parents can remember events in their lives.
You should never feel guilty about being able to give your child so much of your attention.