Layering is how one wardrobe covers more standards and more weather. Three rules that make it work instead of bulk.
The layer against the skin should disappear - a light shell, no texture. The visible layer carries the warmth and the structure. Two thin layers beat one thick one for drape.
A shell under a lower neckline, a cardigan over a shorter sleeve - most "almost modest" pieces are one layer away from working. Check the neckline first; it is the hardest thing to fix with a layer.
Layers in the permanent palette mean any shell works under any dress - no morning arithmetic. This is the palette page doing practical work.
The right layer doubles a wardrobe - without buying a second one.