Why the fiber matters more here
A body pillow is a lot of cloth against you.
A head pillow touches your face and one hand. A body pillow runs the length of you, so the case is against your chest, your arms and your legs for eight hours. Whatever that cloth does with heat and moisture, it does across a much larger area of skin.
That is the argument for organic cotton over a blend. Cotton moves moisture away from you and keeps moving it, where polyester holds it at the surface and turns clammy. Ours is long-staple, which means the fibers are long enough to tuck their ends into the yarn instead of working loose and pilling where the pillow rubs.
300thread count, in a sateen weave
Long-staplecotton, which is what resists pilling