If you’re petite - they need to be slim fitting and above the knee, some of mine are bodycon with elastene. The big chunky knit ones don’t work on me or the midi/midi long - you have to be tall for those
I would disagree that you need to be tall for midi/longer dresses. I am 5 foot 1 and they suit me perfectly. I used to wear short things when I was younger, but I now prefer longer. I agree with you about the big chunky ones not working. I am slim and flat chested as well as being short, in case that's helpful to anyone else. I prefer them to be be merino, though some of mine have other things mixed in with the wool. My favourite merino ones are from Hobbs and M&S (I bought the M&S one for £8, unworn, in a charity shop). I also have a Boden merino one in 3 different colours - must have bought them in about 2010 and they're still going strong. I've also got a Ralph Lauren one which is cashmere/merino mix (had 75% off).
My current favourites are two which I bought in the Boden sale last year - probably supposed to be knee length, but midi on me. They have buttons all down the front (top buttons are all 'fake' and just for effect) and are belted. My absolute current favourite is my dark red Hobbs merino one - open necked 'shirt' style, but completely unadorned apart from a self-colour belt. I love this dress so much!
I wear them all with flat black slim-fitting knee high boots and long socks, with a slip underneath (hate tights). If it's freezing, I add leggings, but nobody can see them under the midi dress and long boots. I'm not going to be making fashion waves any time soon, but it's a look that suits me 100%.