Who’s last name should our son have?

My boyfriend and I are expecting in October. He has a daughter from a previous relationship and she has his name. We just found out last week we are having a boy! We are both thrilled. We have chosen his name but my boyfriend is stuck on giving him his last name after asking him countless times if I can give him mine since it is less common and we only have one male in my family able to pass it on. His family is ALL males with the exception of his daughter and they all have his last name. His last name is also SUPER common. I would really love to give our son my name to carry on someday. His first and middle name are family names for my boyfriend so I wanted to at least give him a part of me too. I did tell my boyfriend if we ever get married we can both change our names to his but I’m not entirely stuck on that happening any time soon. I do understand this is his first and maybe only son and that he would like to give him his name but I think my reasoning is fair. I wouldn’t mind giving him both only it would make for a VERY long last name lol. Mine has 10 letters and his has 7. And they don’t sound very good together.