[MamaS]

That is really not the sort of decision that should be based on "a bad day" or "the terrible twos". Wail until your husband is over his surgery. Then get a sitter and go out alone somewhere. Or, send Joanna to the park with a sitter and sit down at the dining table with all phones off, and have a talk.
Talk about the pros and cons. You might even want to have a list of all his objections -- too old, too poor, house too small, etc. and a list of the positives. Sibling for Joanna when we are gone, don't need a lot of "starter stuff" cause we already have it. If it's another girl they can share toys, clothes, etc.
Really listen to each other, and then come to an agreement. After you reach an agreement - whatever it is - the subject is closed. No canceling for "a bad day" or any other reason except major catastrophic life changes.