Weight is the first decision — a fine-gauge knit layers cleanly under a blazer, while a heavier gauge works as a standalone piece over a collar. Merino wool regulates temperature better than cotton blends, making it the safer year-round choice.
Fit should sit close without pulling — a knit that's too loose loses its shape by the second wear, and one that's too tight limits what you can layer over it. Get those two details right, and one good knit will outlast a drawer full of trend pieces.