Refashionista: Adding a zipper embellishment to a low back dress

I'm a sucker for low back dresses. I just love them! Which is one of the reasons I reached for this comfy knit dress at the thrift store. It didn't hurt that it only cost me 1,5€ either. But, after a couple of wears it started to bother me that the shoulders kept sliding down. So, I figured I needed to figure out how to fix that, because I know I won't wear it when it's uncomfortable.
Then after considering different options, the zipper solution just came to my mind and I knew it was just what I was looking for.

 Here's the back before I altered it. I knew I didn't want to just cover it up, but add something that would add to the awesomeness of the original dress.

 Here's what I did:

First, I measured the distance across the back opening diagonally, because that's how I wanted the zippers to be placed. This gave me an idea how long my zippers needed to be.

I used two 16cm long zippers, although the measurement from the first step was 18cm. I just couldn't find a zipper in the right color in the correct length. But I worked out ok.
I placed the zippers diagonally unzipped and in a criss-cross to each other. I think the picture explains it best.

 Then I placed the ends of the zipper under the edge to the wrong side of the dress and pinned.

Finally, I sewed the zippers to the dress from the right side sewing right on top of the existing seam to make it less noticeable.

Love the outcome! It's just what I needed and the zippers add a little bit of edginess to the dress as well.

Thanks for letting me share!
xo. Hanna