The thing nobody tells you about a little black dress is that it isn't the dress you wear out that matters, it's the dress you can still see the shape of after six months in a drawer. A cheap one goes thin at the seat first, that faint sheen that catches under any light stronger than a lamp. A good one just goes slightly softer, like it's settled into you rather than given up.
On its own it's nothing, which is exactly the point. Throw a denim jacket over it for the daytime and it stops looking like an evening dress at all. A good coat, bare legs and boots takes it from a Tuesday errand to a Friday without you changing a thing. The ones worth having are the ones that don't argue with whatever you put with them, no fighting for attention with a necklace or a bag, no sulking if you add tights instead of going bare legged.
Hand on heart, the difference between the two pound stretch of fabric and the one with a bit of weight to it shows up around week three, not on day one. The cheap version creases the second you sit down and never quite drops back. A heavier jersey or a proper crepe holds its line, washes without pilling at the inner thigh where tights rub, and still looks like a dress rather than a bin bag by the time winter comes round again. Hand wash or a cool machine cycle, dry flat, and don't be tempted to tumble dry it even once, that's the one thing that ages it overnight rather than over years.
If you've got none in the rail at all, start with a simple shift, knee length, sleeves that hit just above the elbow. No zips at the side that dig, no cutouts you'll think twice about at a funeral. It's the version that goes to the most places without asking you to think about it first, and the one you'll reach for when you genuinely don't know what the occasion calls for.
It covers more ground than people give it credit for, a work do in November, a wedding in June with the right jacket, a dinner you said yes to without checking what it actually was. It's not a summer dress and it's not trying to be, but from autumn through to spring it will quietly outwork almost everything else you own.
A little black dress earns its reputation the dull way, by being right more often than it's wrong.