Measure yourself before you buy, not after, and measure with shoes on, the actual shoes you intend to wear, because an inch of hem is the difference between a dress that skims the floor properly and one that frays through at the back within a month of pavement contact. I've sent two back for this reason alone, both lovely on the model, both a trip hazard on me. That warning aside, there's nothing else that does what a floor length dress does. It makes an ordinary Tuesday feel considered without any extra effort beyond putting it on.
It doesn't want fighting with heavy boots or anything too clumpy underneath, the whole point of the length is a long clean line and a boot sole changes the proportion completely, so flat sandals or something slim works better than you'd expect. Avoid piling on a cropped jacket that cuts across the midpoint too, it chops the dress in half visually and undoes the reason you bought it. As for wear, a well chosen one softens with washing rather than going limp, the fabric should relax into the body after a few wears instead of clinging stiffly like it's still on the hanger, and a hand wash or a cool gentle cycle in a bag keeps the hem from fraying at the point where it meets the floor, which it will, eventually, no matter how careful you are. I've had one go soft and lovely after a summer of wear and another turn into something resembling a tea towel after a single hot wash, so read the label and believe it.
The difference between a good one and a disappointing one is mostly in the weight of the fabric and how the seams sit. Cheap floor length dresses are often cheap because they've skimped on fabric width, so the skirt doesn't move, it just hangs there looking a bit sorry for itself, whereas a proper one has enough fullness that it swings when you walk and pools slightly rather than clinging to the legs. Check the hem is actually finished, not just overlocked and left, and have a feel of the fabric between your fingers, it should have some substance and drape rather than being thin enough to show every seam of your underwear in daylight. Zips and poppers should sit flat, not pucker the fabric around them, because that's usually the first sign of corners cut elsewhere too.
This suits anyone who wants to feel dressed without being fussed over, whatever her age or the occasion in front of her.