We have bought more sheets than I can count hoping they would stay on our king mattress. None worked until we purchased the Cool & Lazy Sheet Set. They are the most expensive sheets we have ever owned, but well worth the money.
We have had them for on for a week and they have stayed on perfectly. Just washed them yesterday and used some OxyClean, dried them on a low heat setting and they came out snow white. A little wrinkly but once on the bed, they are fine. We live in the south and we have the AC set on low, a ceiling fan and a small fan on my nightstand and we still struggle with sleeping because our old sheets still felt hot. These sheets are always cool and we love them.
One minor suggestion. Wish there was an option to make the sides and bottom of the top sheet shorter and the head of the top sheet longer. The sides and bottom hang down too far and at our age we don't want to struggle to tuck them in - that's why we like the top sheet design.
We highly recommend these sheets!