Arm Sleeves
Low-friction gaming arm sleeves from FLUXAIM. They do one job and they do it completely: they take your forearm off the pad surface so nothing you do with your arm changes how your mouse moves.
Forearm drag is a real and underrated variable. Bare skin on a mousepad grips unevenly, and the grip changes as you warm up and start to sweat, which is exactly when a long session starts to feel worse than it did in hour one. A sleeve makes the contact between your arm and the surface constant, and it keeps sweat off the pad so a cloth pad stays fast and a glasspad stays clean.
If your aim visibly degrades late in a ranked session, this is one of the cheapest fixes available to you.