It always wants to ride up the sides of my bed because elastic never wants to hold it in place. When I wash and dry my sheets it inevitably spirals up in the washer and dryer so it never washes or dries properly. Then it’s a pain in the ass to try and fold neatly.
I feel like I’m failing adulthood after being bested by a bedsheet.
Mattresses have an enormous variance in thickness, and sheets vary considerably in the depth of the “pocket.” If your sheets can barely fit over a too-thick mattress, then they’re going to pop off when you move on them. You might just want to buy some new sheets with a deeper pocket. Alternatively, you can buy elastic straps that go under the bed and clip onto the sheets. You’ll generally either find these as a four pack of short ones that are meant to go only at the corners, or as a two pack of long ones meant to stretch under the entire bed and attach opposite sides. Get the long ones; they generally perform much better.