Castelli Perfetto Vest:
https://www.castelli-cycling.com/us/...451650819P-034
The best vest I have owned. Throw in head thingy, and it is quite comfortable in 40s. One note Castelli do run on slim side of things.
Another Alternative:
https://www.castelli-cycling.com/us/...451650619P-085 Slightly warmer then vest + arm warmers. Can take sleeves off when it gets warmer.