A lot of us have been there!

Im about to have my second baby. This is my husbands first child. I have a son from a previous relationship. He wants another baby after this one but i am dead set on no more children. The deal was if it was a boy hed be satisfied with not having more children, and luckily its a boy. But hes starting to rethink thia deal. Pregnancy is insanely hard and rough on my body and i am very certain i dont ever want to go through it again. I also am very career orientated and the troubles with this pregnancy made me turn down my dream job. If we wanted another later in life, id prefer to adopt, which my husband is open to but obviously doesn't want to have to do it. How can i convey my feelings to him better about this without seeming like im being selfish?