High-waisted bottoms, denim layering, statement accessories, and oversized outerwear all have modern equivalents sitting in most closets right now
58cm based on a UK size 8 (longer length, centre front point to hem approx 63cm based on a UK size 8)
A lightweight plaid shirt tied around the waist also adds color while preparing you for cooler evening temperatures
That being said, if you find yourself attending an increasing number of Black-Tie Optional events, it may behoove you to purchase a complete Black Tie ensemble so that you are well-prepared should you receive an invitation to a strict Black Tie event, for which a Black-Tie Optional ensemble would not be appropriate
While they can be tricky to track down, Amazon's official fashion section is always a great place to start
What you need: A black dress, mouse ears, a red bow, face makeup, and pearl jewelry