Quality knitwear is one of the wardrobe categories where mid-tier brands often beat premium for cost-per-wear. The signals to look for are simple once you know them.
What to check
Ply count (2-ply minimum for cashmere, 4-ply for serious quality). Fibre source (Mongolian cashmere best). Construction (fully fashioned seams, not cut-and-sewn). Weight per square inch (heavier knit lasts longer). M&S Autograph cashmere, Uniqlo cashmere, Cos wool jumpers all hit these markers at £80-200.
Skip £400+ luxury cashmere unless you specifically want the brand. The mid-tier delivers the quality without the brand premium.