You could try a matrix of droppers all dropping into the same hopper (connected to a comparator), but that system does introduce a lot of lag and is not easily resettable.
You could also make a huge block of observers curving around each other, so that for each column the bottom button has 2 observers, one facing toward the button and one underneath facing the first observer, and each row above would have more observers to "curve" around to bottom.
Lastly, you could use a calibrated skulk sensor behind the matrix hooked up to a lectern/comparator combo with the book inside set to page 10 (of 15). This will calibrate the CSS to only recognize pressing buttons, turning on levers, opening containers, priming TNT, opening a door or fence gate, playing a note block, or setting a tripwire.
If it's not intended or possible to do those in the range of the sensor, this option is the best because it uses minimal lag, is small, and resets itself. (Keep in mind you can use wool blocks around the sides of the sensor that you want blocked in case one of those sounds would occur on a different side of the mechanism.)
There's probably a lot more solutions to this, some of which would be better than these. I hope this works for you!