Do you ever have those middle-of-the-night moments, when you wake up and remember something odd? Now, I wear mostly traditional plain dress, and like it, but some of that is adapted from modern clothes, like a jumper over a plain longsleeved dress, practical and modest. And I prefer traditional fabrics like linen, wool, and cotton denim.
But maybe if you are looking to “get started” without going all out, this is a source I suddenly remembered from my childhood: Vermont Country Store. They have an online catalog, and they are a source still for traditional jumpers and dresses, some in knits, pretty feminine prints, and the sort of ordinary stuff my mother and her friends wore. This is not an endorsement in some way – I haven’t purchased from them in years, but they have an excellent reputation. Their US prices are a bit high for my budget, but one could put together a good, modest, almost plain work wardrobe without paying those outrageous mall prices.