Second Child

My son is nearly 21 months old now. Many people asked us whether we would have a second child. We know it is good for our son to grow up in an environment where he could learn to take care of others and to share, but then my (selfish) feeling is that it is going to be challenging for me to raise another baby, both physically and financially. Lack of sleep and rest is the major reason for my hesitation. My son can basically sleep through the night now, after a battle of 20 months. Should I go and destroy this equilibrium again and let myself "suffer" for another 20 months?