Universal Knife Sharpening Stone w/Dual Grit 1000/6000 for Kitchen Knife Set, Chef Knife, and more - Whetstone Sharpening Kit with Angle Guide, Non-Slip Silicon and Bamboo Bases by ROYAL CRAFT WOOD

The brand doesn't matter, just the grit and make sure it's got something around 1k/5+k grit on opposite sides. The one I got has a friction pad on the bottom of the base and I can't recommend that strongly enough, that one has done good work for me for a decade, it was like ten bucks. EDIT: Something like this is what I use. Simple and cheap but it has done me no wrong.