I am not sure I understand your post.....Do you want another child for your son or for you? What does your hubby say? It is a joint decision.
Your health is priority, especially if you want to be around for your 3 yr old to grow up.
I have a 14yr old daughter, only child, no step siblings or anything and we have a very close, tight family. People ask her if she is sorry she has no siblings and she is adamant.... NO, she loves it this way. My house is always full of kids, especially on weekends. Sometimes it is like we have 3-4 kids, LOL
We did not have her to secure our retirement or take care of us when we are old......we had her because we wanted a child to love and raise. Our family was complete with 1 child and we have no regrets.
There are opinions both ways about only children....yes, my daughter has everything she'll ever need, more importantly support and unconditional love from her parents. She is not some spoiled brat...we nip that behavior when we experience it (YES, we see that pop up on occasion). She is well rounded, very social, and honors student planning for her college at this time.
She went to preschool, met friends and still has some friends from preschool. If you just want a playmate for him, join a play group, preschool, make friends for him.
The choice is for you and what is right for you, Best wishes to you.