Should baby have my last name or step fathers last name?

Okay so i got pregnant with my ex boyfriend, we broke up and i didn't want anything to do with him i wanted to do it on my own rather than with him. Now i'm almost 29 weeks and i'm with someone else and have been for a bit now. We're planning on getting married like next year sometime and we've been talking about getting engaged soon, i think he's already bought the ring just waiting on him to ask. Anyways, he's been super supportive of my pregnancy and he's super excited to have a little baby with me even though it's not biologically his. He plans to adopt my baby after we get married, because he wants to and because he's in the Air Force and the baby wouldn't be covered under his insurance if he doesn't. So what i'm trying to figure out is should i give my son my last name still or should i go ahead and give him my boyfriend's last name? I obviously have some time to decide since i still have 11 weeks left but i'm just not sure.