I don't want any more kids..

My mindset may change, my first son is only 4 months old. But as of right now, I don't see myself ever wanting any more kids. My husband and mother are so upset with me for this, saying I'll need to give him a sibling in a couple of years and trying to make me feel bad for making him an only child. I really love my son and love being a mother, but I just don't see myself having more. Like I said, I may change my mind down the road but if I don't, is it so awful that I'm content with this one baby?