I like the Ibex "woolie" tops as a thin merino under layer, and also to sleep in! Very soft and snuggly but not heavy. (Ibex woolie tops run small so DON'T order smaller than your normal size)

I like the Smartwool Hoodies to throw over my base layers during cool bike rides. The hood is thin and snug and fits wonderfully under my helmet. (Get 1 size smaller size than you usually order- the hoodies run large, unlike other SW items.)