For years I thought a cowl neck was just a slightly fancier crew neck, and bought the first one I tried in a changing room with bad lighting and worse posture. Put it on properly, standing up straight in front of a decent mirror at home, and the drape actually did something, it fell in soft folds instead of sitting flat like a bib. Posture is half the fit with these, which nobody tells you.
A fussy necklace is wasted under one of these, the cowl is already doing the jewellery's job, so anything chunky just gets swallowed in the folds or clatters about annoyingly when you move. Same goes for a big statement bra strap peeking out, the draped fabric gapes more than a standard neckline and gives you an accidental view most of the day, so a lower back, racerback, or at least a strap in a similar colour saves you fiddling in public. On sizing, go for your normal size rather than up, because cowl necks are cut generous through the chest already and a size up just means more fabric pooling and gaping when you lean forward, which you will do, reaching for something on a low shelf, bending to pick up a bag, and suddenly you're giving a stranger more information than planned. If you're fuller busted, look for one with a slightly higher starting point at the shoulder rather than a deep scoop, it keeps the drape decorative instead of alarming. The honest limit is that this is not a dress for anything structured or corporate, it reads soft and a bit undone even in a smart fabric, so wrong for an interview or anywhere you need sharp lines. It is also not kind to a very short torso, the extra fabric can make you look like the neckline is wearing you rather than the other way round, and on anyone with a lot of width through the shoulders it can add bulk exactly where you don't want it.
What surprises me is how a cowl neck dress ages well in both senses, the fabric softens with washing so the drape gets even more fluid rather than stiff, and the style itself doesn't date the way a lot of dress shapes do, because it was never chasing a trend to begin with. Mine from a few summers ago drapes better now than it did new, slightly worn in, slightly more forgiving, which is more than I can say for most things that live in my cupboard that long.