The acrylic fabric used by DeFeet (yes, the sock people) is beautifully soft.
It's also exceptionally springy so it doesn't bunch but stays in contact with your skin when you move, effectively drawing moisture away and drying quickly when you work up a sweat. The cut is close with a long body to prevent draughts but we'd prefer a higher neck. You don't get tons of insulation so you'll need a good jersey to provide the warmth. Also available in short sleeve (£23.99) and sleeveless (£19.99) versions.