Back in the kde 3 days, there was this applet called "knob" for volume control. For me personally, its circular knob UI is actually the best.

Firstly, you can place the applet at a corner of the panel, e.g. at the bottom right, such that you now have an infinitely large target [1] to hit.

Then, once you have the mouse pointer hovering above it, you can:

- scroll up/down to increase/decrease the volume

- middle click to toggle on/off the sound

For those who possess precise control of the mouse pointer, of course they can still click on an arbitrary spot on the knob to set the volume.

For bonus point, because it is a knob, you always know what is the current volume level. All that for maybe 40x40 pixels of screen real estate only.

[1] https://blog.codinghorror.com/fitts-law-and-infinite-width/