For a premium tee use a combed cotton single jersey with fine yarn, 180–220 GSM. The extra weight gives drape, opacity and a pleasant hand, while combed yarn reduces pilling and makes the surface smoother. Also check the evenness of the knit, because flaws show immediately on a clean-looking fabric. A premium tee also needs good cutting, neat stitching and a rib that holds the neckline, so choose the matching rib too. Ask for samples in two weights and compare them on the body, not only in your hand.
What fabric should I use for a premium t-shirt that looks high-end?

premiumtshirtcombed
Fibres & yarnsCan single jersey be made with linen and how does it behave?
Yes, single jersey with linen exists, usually blended with cotton or viscose, for example 55 percent linen and 45 percent cotton.
Fibres & yarnsCan single jersey be made with wool and how does it behave?
Yes, single jersey with wool exists, often blended with cotton, viscose or polyester, for example 30 to 50 percent wool.
Fibres & yarnsWhat does melange (heather) mean in knitwear and how is it made?
Melange is a mixed-shade appearance with a slightly speckled yarn effect, typical of heather grey.