Layering
I got a Patagonia very thin longsleeve baselayer some years ago, for those cool spring and fall days. It's very lightweight, way thinner than t-shirt material, and works great under a short sleeve jersey. And it's comfortable under a shirt for winter wear off the bike. I like it.
So I got a second one. What I didn't expect is how effective two thin layers are. I guess the outer layer slows the wind, making the second layer much warmer than expected. Either of these is very breathable and doesn't block much wind, but two together are effective down to the low 50F range. Surprising.
As it gets colder, an uninsulated cycling jacket with various base layers stacked is good for a wide range of riding temperatures. I have thicker base layers, these ultra thin ones, and recently got a thin fleece zip shirt.