Check out the back of Anahita’s dress….
Anahita’s dress is from Topshop. The necklace is vintage (and stunning). The bag is Dolce & Gabanna.
The back of her dress is so damn ethereal to me. I find good ones here or here.
Outside of eBay, the best vintage style necklaces I’ve seen to layer over a basic dress or T-shirt: this, this, this or this one.