I remember the exact pair that converted me, dark denim, rigid at first, worn with a plain white t-shirt tucked in and nothing else going on. I bent down to pick up a toy off the kitchen floor and there was no gap at the back. None. I actually checked twice because I genuinely thought something was wrong with the mirror. That's the whole appeal of a proper high rise, it sits where your body already curves in, so it stops the gaping that low and mid rise jeans do the second you move.
They change a lot over the first few months, and you have to let them. Rigid denim will feel stiff across the front of the hip for the first few wears, almost like cardboard, and that's not a fault, that's just unstretched cotton finding out what shape you are. Give it two or three wears and it softens and moulds, especially through the thigh and waistband. Stretch denim behaves differently, it's comfortable from day one but it can bag out by the afternoon if the stretch isn't the recovery kind, the sort that pings back rather than just giving up. Wash them inside out, on a cooler cycle, and skip the tumble dryer if you want the shape to last, because heat is what kills the stretch and leaves you with jeans that are loose by lunchtime and loose forever after that.
The difference between a good pair and a disappointing one usually shows up in the waistband and the seams before anything else. A well made high rise has a wide, sturdy waistband that doesn't roll or fold over when you sit down, proper bar tacks at the stress points, and a zip that doesn't feel like it's fighting you every time you do it up. Cheap ones often have a thin waistband that curls, and seams that pucker after one wash. Hold the denim up to the light if you can, you want it close woven, not see through, with a bit of weight to it. Lightweight denim looks fine on the hanger and feels thin and flimsy by the second wear.
If you've got none of these, start with a straight leg in a mid weight stretch denim, dark wash, no distressing. It forgives more body shapes, hides a multitude of post lunch sins, and doesn't shout about trends that'll feel dated in two years.
Try sitting down in the changing room before you buy, standing up never tells you where the gap really is.