macys maxi dresses Msk Women's Long-Sleeve Dress and a wide I.N.C. International Concepts Women's Linen
Description
Stick to unlined or lightly lined options to avoid trapping heat
wide non adjustable straps

That being said, you don't have to wear a dress to be dressy

See long plus-size formal dresses for prom and La Femme designer plus-size evening gowns with a-line skirts and slits