I have a mate who has four kids to her ex husband (he has actually died now) so they all have the same name but she has since had another bub to a different guy (who does not live with her) and didn't know what to do about the surname becuase she didn't want her youngest to have a different name to the other kids. In the end she went with the father's surname as he is in the baby's life. My ex had a child from a previous relationship and her mum gave her the surname of a boyfriend she then broke up with! So the the kid had name that was not her mother's or father's!!! If I was in your shoes I would go down the maiden name route so you have the same name as bub and it is not your XH's name (he has nothing to do with the bub after all).