Hey there HeavySleepah,
What’s happening is your fitted sheet isn’t creating enough downward tension to “lock” the protector against the mattress. When you roll, the sheet shifts slightly, and the protector moves with it. The thicker the mattress and protector combo, the more important that tension becomes.
Sheets that fit tight like ones with strong elastic and deep pockets, solve this because they compress everything together so it moves as one unit.
For example, DreamFit sheets use four extra-strong corner elastic bands that anchor under the mattress. When they’re on, they fit almost like a drum, very taut, so my sheet, cuddledown wool mattress protector, and even my topper don’t shift at all. On my master bed, they hold everything in place.
That said, it’s not only about one brand. I have a Glacier Sleep Apex in my guest room with a Malouf protector and California Design Den Egyptian cotton sheets, and I don’t have this issue there either, because that sheet set fits tight enough.
Bottom line: it’s about sheet tension. The tighter and more securely anchored the fitted sheet is, the less anything underneath will slide. I will admit, the DreamFit sheets are quite a bit more expensive than those Ikea sheets, although mine are the Egyptian Cotton, but even in long staple cotton, they still fit tight as a drum. The CDD sheets are a bit more than the Ikea, but still under $100. I am surprised you have a great mattress, excellent mattress protector, but went exteme budget on the sheets,
Another option you may want to look into is either a body pillow or use a king pillow as a body pillow to keep you from rolling around. The @Glacier Apex is an excellent mattress. It is one of those that if you saw it expanded next to a mattress that does not come in a box, you would never know the Apex did come in a box. The look, feel, comfort and long term durability is all there in a very nice package. The one weak link in your set up is the sheets.
Just my perspective on this,
Maverick