If you want to keep your shoulders warm when wearing a strapless dress, but don’t want to ruin the effect by wearing a sweater or jacket, a good solution is to wear a shrug. These are sort of bolero-style jackets, sometimes just long enough to cover your shoulders, sometimes longer, that are made to complement the dress you are wearing, rather than hiding it like a regular jacket would.
The version on the right is more of a jacket than a shrug, but I included it because it looks so nice:
Plus-size silver shrugs pictured:
Left: Torrid Silver Slinky Shrug
Right: Yoursclothing Womens Plus Size Silver Foil Print Crinkle kimono Shrug With Wate, cream