i asked a similar thing in the autumn, albeit looking for a more winter focussed one, and was thinking about merino myself. my concern though was that i froze on a road bike and that merino would let the air through.
a couple of people suggested castelli gabba, something i had not heard of, and i have to say it is an utter revelation. i never ever though that i could tide well under 10deg (i think the lowest was down around 4deg) in a thin short sleeve with arm warmers and a couple of base layers.
so personally i’d say, for now into summer if a gabba is too warm, go look for a perfetto light. there are some bargains about if you look. i think i paid under 60quid for mine.