Use the overshirt as a layer
Worn open, an overshirt adds a line without the formality of a jacket. It works best when the top underneath is simple and long enough.
Allow for the thickness of your T-shirt or knit. An overshirt that pulls at the shoulders does not become more comfortable just because it is casual.
Balance the volume
If the overshirt is relaxed, choose straight jeans or trousers with a clean line. You can also do the reverse with a closer-fitting outer layer.
Change one volume at a time. It is easier to see what works and reuse the pieces in other outfits.
Let the shoes suit the day
Light trainers make the outfit easy to wear in town. For a longer day, check width, support and the sole instead of choosing by colour alone.
Raw denim can bleed in the wash. Check stretch, length and care instructions before choosing.
You may not need to buy anything
Start with a thick shirt, light jacket or cardigan already in your wardrobe. The goal is to use layering, not to recreate a picture.
If you are truly missing a piece, choose one you can wear with at least two bottoms and two tops.