Sheets and other bedding should always be of the most quality that is appropriate to a budget.
Thread counts of sheets will relate well to comfort. This indicates how many threads are woven into each square inch. A high thread count provides smoothness, with a luxurious touch. High thread count sheets will be strong and durable.
Sheets quality is also indicated by fiber composition. Linen sheets made from flax and can best for summertime. Somewhat expensive and needing special handling, linen sheets can be an investment for longevity.
Most popular these days is 100% cotton bedding. It is practical in any climate. It gets softer with laundering.