It's up to you (if you can both agree!).

I'm married but didn't change my name. Our bubba will have DH's surname. He didn't care either way but I sort of felt it should be that way (just personal opinion).

I know from my MIL's experience though in NSW, if you decide to give your bubba your DP's surname and then decide in a few years time to change it to your surname, you will need DP's permission until your child is 18.