If you get switches from a reputable supplier you can check the datasheet, the parameter will be called activation force or operating force, and is measured in newtons (typically). Lower number means less force needed.
If you get your switches from cheap china sources, you can expect these numbers to be completely useless. You could instead achieve less force with some kind of paddle or lever. The longer the lever, the more distance you need to move it to press the button, but the less pressure required. 3d printing back paddles makes this trivial if you have access to one as you can make them any shape you want.
