During the coldest part of Mn (generally the last week of Jan and first wk of Feb is the coldest for MN), My favorate beaches would be any beach in Hawaii . . . .
Waikiki, Ka'anapali, and this season "some beach" on Kauai ~
We've been to Mexico (Cancun and that area of mexico ) a couple times - it's just not the same weather and can be cool. It just isn't the USA.
Florida can be too cool to soak up Vit D
As can California . . ..
Wife likes to get her share of Hawaiin Vit D to bring home - It cost's a bit more then the pill form out of the Drug store ~   lol