The plainest dress here and the hardest to buy. A sheath has nowhere to hide: no gathers, no fullness, no waist seam to disguise a fitting error. Which is precisely why it is the strongest argument for having something made — off the rack, this shape fits almost nobody without alteration.
Why it works
A bateau neckline runs wide and shallow across the collarbones, which balances a narrow frame and looks composed rather than dressy. The elbow sleeve covers the upper arm without heat. Knee length reads as work-appropriate almost everywhere.
Notes for your dressmaker
Ask for a toile. On a sheath it is not optional — the difference between a good and an approximate fit is entirely visible. Choose a crepe with a little stretch for comfort, and add a back vent or the hem will restrict your stride.