Vintage (1970s/60s) sleeveless sheath dress

From my grandmother's closet! In very good shape. Navy blue and white. No contents label, likely synthetic material. No pilling or significant signs of wear, other than a few faint spots on the white stripe; see photos. Inside shots show workmanship; seems handmade but for the label. This is big on me (I wear size 6), so thinking it would fit size 8 or possibly 10. Consider MEASUREMENTS — Armpit to armpit: 18.5" / narrowest point around waist: 16.75" / Length, shoulder to hem: 38.5"