What size mousepad should I get for low-sensitivity arm aiming?

Get the biggest desk pad you can fit — ideally 900x400mm or larger (standard “extended” or “XXL” size). Low sensitivity requires whole-arm movement, and a small pad forces you to lift and reposition, killing consistency. Most cloth pads that size are cheap ($20-30) and last forever, especially with stitched edges. Just measure your desk first to avoid overhang.