Many years ago, I used to struggle in buying bed sheets. The “thread count thing” was confusing to me thus, I would always end up buying higher thread count sheets and still wound up not so pleased with my purchase. I learned through the years that when buying sheets, the thread count is not all that matters, it certainly does not tell us the whole story. Why? Because it does not always indicate softness and durability. The quality and length of a yarn as well as the type of fiber and the origin of the cotton used also contribute to the texture. Hence, two 400 thread count sheets may feel very different. In fact, many experts suggest that when we buy sheets we should consider yarn quality and cotton type before the thread count.
We all know that poly blends are cheaper and lasts longer and they are also more stiff and less comfortable than 100% cotton. Supima cotton which has long and soft fibers and Egyptian cotton(the mix of short and long fibers makes it soft and durable) are excellent choices.
As for the fiber, ring spun cotton fibers are twisted to make the yarn stronger while combed cotton are the best because the process of combing leaves will leave the softer and longer ones.
Sateen sheets are the softest. If you prefer the plain weave it is coarser. Twill and oxford are slightly softer.
And the thread count? If money is no object, you can go as high as 1,200. But based on experience, when I touch my sheets that are at 800TC and compare it with those at 600TC (and that is after many years of use) I can not really tell the difference. I just rely on my sense of touch and since then, I’ve been happy with my sheets purchase all the time. I always go for ring spun, combed, sateen, Egyptian cotton sheets at 600TC or 800TC depending on the feel.