Why long-staple
Long fibers make a cloth that survives the wash.
A cotton fiber's length decides how the yarn behaves. Short fibers leave ends sticking out, and those ends work loose in the wash, ball up, and become the pilling you feel under your hand after a year. Long-staple fiber tucks its ends into the body of the yarn, so the surface stays smooth.
It is stronger too, which matters most for the fitted sheet. That piece gets stretched over a mattress a couple of hundred times a year, and it is the one that gives out first in almost every set. Ours is long-staple organic cotton in a sateen weave, which puts more of the yarn on the surface and gives the drape without a chemical finish.
300thread count, which is the useful range
Sateenweave, soft without a finish
The whole bedding range