Ideas..

Agreed! I wouldn't add anything to it! The top has so much detail, and the bottom is also full of texture, adding anything else could make it a bit busy. Your jewelry will add plenty of needed sparkle!

Amazon is usually a great place to find undergarments!

I would not add anything too it. There is already a lot going on and I feel like adding anything, specifically a belt, might be too much. However, if you really want to add sparkle, you could add straps that sparkle, or have your seamstress add sparkle to the skirt.

I had a layer of glittery tulle added under one of the layers of my dress, but my dress didn't have the layered effect like your dress nor did it have the pretty design at the top like yours done. I would add sparkle with jewelry rather than to the actual dress.

I tried on a dress similar to this, but the waist wasn't a drop waist and that had a belt. So maybe you could add one but I wouldn't! I think it looks beautiful as is! You could pick more sparkly jewelry and accessories to add more sparkle to yourself instead! Maybe do a hairpiece of some sort.

If you wanted more sparkles you could add the belt like you said. You could also add a sparkly veil and sparkly jewelry as well to compliment your entire look.