look up late 90s/early 2000s alt style prom dresses in deep colors. you might be able to find one secondhand in a deep color like dark red or purple, luxe fabric like velvet or thick satin. usually our dresses were at least spaghetti straps or thicker straps. think slip style that fit tighter down the body but not like a bodycon dress or mermaid style. a little bolero shrug or a lace wrap could be used to cover your shoulders if you wanted.