Over the knee boots or OTK boots as they are known can be tricky to pull off. I bought a pair a few years ago and it made me look like puss in the boots. I looked awful and thought my thighs were too large for this type of boot. BUT it really comes down to the style of the boot.
The ones that have a slit up top like this Kendall&Kylie pair here will make your thighs look bigger. The top just widens in a way that is really unflattering. Unless you have really skinny legs, I’d avoid this style.
This pair by Abound doesn’t have a flap up top but it doesn’t have a lot of structure meaning that as you walk the shaft will slide down and bunch around your leg a bit, making your leg look wider and thicker in some areas. Not a good look.
Last thing to keep in mind is the height on the shaft, it should be over the knee not crotch adjacent. It just looks too Pretty Woman to me. Stuart Weitzman is the kind of OTK boots but these boots by him are kind of blah. I am also not a huge fan of high heels or stiletto heel on these boots as this a strong look on its own, adding high heels really takes it to whole other level. Being 40 and in the suburbs, I stick to flat or small (under 3″) block heel.
I like this pair here by Stuart Weitzman, its pretty pricy at $798 but if you look around they go on sale, esp as spring approaches. Charles David Gunter boots are much more budget friendly here. I also love these (look better on than they photograph) Steve Madden boots here.
As far as how to wear them, my perennial fave is over skinny jeans or with a sweater dress. If you want to look skinnier, go monochromatic meaning black boots w black jeans, beige w beige or even white on white.