Hold one up against your leg before you even try it on. That shape, close from hip to ankle, is either going to feel like a second skin or like you've been sewn into it, and the only way to know which is to get the denim moving, sitting, bending, before you decide anything else about it.
If you've got none in your drawer right now, start with a mid or high rise in a dark, plain wash with a bit of stretch in it. No fading, no whiskering, no rips at the knee. Dark and plain goes under everything and doesn't date the way washes with obvious trend details do, so it's the one you'll actually reach for on a Tuesday when you haven't thought about getting dressed properly.
The difference between a pair that lasts and one that's in the charity bag by spring is mostly in things you can't always see on the hanger. Good stretch denim has some recovery in it, so it comes back to shape after you've sat down for a few hours rather than bagging at the knee for the rest of the day. Check the inside leg seam is flat and even, not puckered, and give the waistband a proper tug, it should sit without folding over on itself. Cheap zips and buttons let you down fast too, a stiff zip or a button that needs pliers is usually a sign the rest of the construction wasn't given much thought either.
For everyday wear, think about what you'd already put with a plain pair of trousers and start there. A crew neck jumper and ankle boots. A white shirt with the sleeves pushed up. A long cardigan if you want to cover the hip and thigh line without losing the shape at the ankle. They go under a longer coat in winter without bulking anything up, and with a plain t-shirt and trainers they're about as unfussy as denim gets in the warmer months.
They earn their keep most in the in between months, when it's too cold for bare legs but too mild for proper winter layering, and they're honest workwear for anything that isn't strictly smart, a weekend lunch, the school run, travelling. I wouldn't reach for them for anything that needs real polish on top, but for most ordinary days they're exactly right.
Wash them inside out, on a cool cycle, and they'll keep their colour and shape for a lot longer than you'd expect.