A thick rough wool zip neck jumper (about £40) over a merino short sleeve base layer and with a gillet on top, covers most circumstances for me. The thick wool cuts out most of the wind on my arms, the gillet protects my chest, and the whole ensemble is more breathable than any cycling specific garment I have bought (and I have a wardrobe full of them). When I steam up the zip gets opened, and the wool is elastic enough to pull up to my elbows. It even handles light misty rain.
For when it’s wet I have one of those Montane Pertex pullover smocks. This folds up to the size of an orange, so it can go in a pocket of the gillet. In real rain there is some dampness, but it’s warm enough.
The only disadvantage for the fashion conscious is that it doesn’t look very mountainbikie 😆