Adapting a pattern - zipper to button closure?

I have a pattern for a girl's summer dress that has a zipper closure in the back. I would like to change the closure to a slit-type opening with a button and loop closure at the neck.  Any ideas on how would I go about doing this?  Thanks!

The simplest way is to topstitch down and around the opening to catch the seam allowance. Hand sew a button on one side and an elastic loop to the other side.

The more proper way of doing it would be to make a facing. I assume there is already a facing at the neck opening? You could probably add to this and sew it all at once. If you do the facing method tuck the loop in between the layers before stitching, make sure to reinforce with some backstitching at that spot.

Hope that helps.