Personally I would never give a child a name of someone who was not their biological parent. What happens if you break up with this guy? Then your child has a name of someone you may never see again. All very well to say you'd change it but a name is part of a child's identity. You can't just change it on a whim.

My advice? Give the child your surname.
I totally agree N2L!
I'm with N2L.

I hope you've had independent legal advice. If you haven't - go get it. Now.
I'm assuming based on her post, that the OP and her DP may have used a donor situation to conceive this child. I think anyone who uses a donor would find what you've all said a bit rude TBH.