I gave my DD the last name of my fiance, and I completely understand what you're saying about needing/wanting to have the same last name as your child. DP & I are slowly moving towards marriage, and after we're married, we'll all have the same last name. I considered giving DD my name until after we were married, but then I thought about two things: 1). how hurt my DP would be that his child wouldn't carry his name; and 2). all the paperwork I would have to go through to change both our names.
I have also heard of what one of the pp suggested: creating a new family name for everyone. I have known people who have done this, and the new family name that they chose was a group effort and the name ended up having a very special meaning for them all. Maybe that will be an option for your family as well.
Best of luck to you, OP.