Getting remarried - SK doesn't want his mom to take my last name

Backstory is I've been with my partner for 6ish years and engaged a year. Both been married before, I have 3 kids all with my last name.she has one boy (8) and he has his father's last name. Partner has reverted to her maiden.

I want my partner to take my last name, I guess I'm quite a traditional person. She is reluctant, basically because her son doesn't want to be the only one in the house without that name.

I do kind of understand his concern. However he is the only one with his father's last name. Still I guess he may feel left out. I also can't help but feel part of the reason he's saying this is because he knows that's what I want so is just pushing back for the sake of it. It came up last night, and in a snarky tone said that mum won't do that cause I don't want her to. I said to him perhaps he needs to consider other people's feelings and wishes instead of his own.

So am I being unreasonable here?