By soft do you mean that it never comes to a point where the lever stops. and comes back against the grip? Or just feels spongy even when the brakes are stopping the bike? When was the last time you changed your brake fluid? Sometimes the brake lines as they get older expand as you apply the brakes and can also give you that vague feeling at the lever or pedal
Are you able to pump them up? Or does it stay soft no matter what?
Is this a new condition or has it always been this way and now you want to do something about it? Any chance you have ABS? I ask about the ABS because my son's machine with ABS has a spongy feel to the lever. When riding his machine, the brakes feel the same, I couldn't tell one machine from the other so his slightly spongy lever has no negative impact on brake performance.