Oxfords, derby shoes, or dress loafers are all great options
Personally, if its optional I think an elegant cocktail dress is totally appropriate

Explore the Features Firm Compression 20-30 mmHg Helps relieve moderate symptoms of varicose veins, heavy legs, pain and discomfort Medical Grade Support Medical grade graduated compression helps to improve circulatory wellness and helps reduce swelling of the ankles, feet and legs Midweight Material Midweight nylon and spandex combine to deliver support and help reduce swelling and leg fatigue Comfort Top Band Wide stretch top band provides comfort and helps keep the sock in place Soft-Seam Construction Designed for comfort and helps prevent skin irritation Fitted Heel and Roomy Toe Knit-to-shape, fitted heel, and roomy closed-toe design deliver comfort and support Recommended for the following conditions: Post-surgery and after vein procedures Help reduce swelling in the ankles, feet and legs Helps relieve heaviness, pain and discomfort in the legs Help improve circulatory wellness and valve function Additional Details Sizes: S XL Compression Level: 20-30mmHg Colors: Black Material: Nylon and spandex Collection: Dr

Sock and Sundresses This outfit has everything the '90s had to offer: flowery sundresses, oversized vests, big hats, and wait...is that a slip
Flattering V-neckline that elongates the neck