A protector is a cheap way to keep a mattress clean, but the wrong size or a crinkly top layer can be annoying. A few checks avoid most disappointments.
Fit comes first
Compare the stated mattress depth with yours. Fitted-sheet style skirts with elastic hold better than simple corner straps.
Surface and washing
Some protectors have a quiet cotton-like top, others a plastic-like feel. Check how the manufacturer says to wash and dry it, because high heat can damage a waterproof layer.