You could try the “Ten Brush Slots” plugin, there you have the ability to put two or more brushes into slots, and if you only put an eraser with a brush into a slot you can cycle “through” those two brushes. The only thing to hope is that each of the two remember its size.
Also, “Buli Brush Switch” may be a way.
BTW: The docker you asked for is the “Quick Settings” Docker.
Michelist