Two important facts to Look for:
1- thread count
The higher the thread count, the softer the sheet, and it will age well, and become soften over time. Good sheets range anywhere from 200 to 800, but ideal sheet is a combed cotton sheet in the 300 to 400 thread count range.
Jersey sheets or T-shirt sheets are made with a flat knit that keeps them soft, but also means they can be slipping, and sliding on the bed. If you live somewhere that gets extremely cold, consider flannel sheets.
Cotton is The best quality. Cotton both traps heat and lets cool air pass through in summer, so it’s a great choice for almost any climate. It can be blended with rayon and other materials that helps its weight and feel. As with any sheets you buy, do a hand test to see how you like these blends.
Look for 100% Egyptian sheets they are soft, and extremely durable. Pima or Supima cotton is known for its softness and sheen and is a little more affordable than Egyptian cotton.
Linen sheets are Perfect for hot climates, they are expensive, but will have a long life. Just be prepared to do a lot of ironing, unless you like the wrinkled look. Although satin sheets look glam and feel romantic, they can be too warm and slippery for many people.