You should get some bed suspenders, they go diagonally across the bottom of each corner of your bed clipping up on the sides to the sheet to hold it in place ! They’re cheap.
@kritiper Just me. The bed sheets were too small for the bed. For some reason washing made it fit better. @Tropical_Willie I have bed clips from BBB bed bath and beyond that I have to put on every time that I wash the sheets. My sheets finally fit. So they aren’t needed for now.
Fitted sheets seem to be made for very thick mattresses these days. I find it hard to find one that fits just right. (Like a 9” thick mattress.)
I had to put some of those bed suspender/clip things to keep my mattress pad on.
Yeah, washing always makes it fit better. I always wash my new sheets in hot water to make them shrink as much as possible for a better fit.