If you truly only have a hardness problem, a water softener will take care of the problem. It doesn't add anything. The media in the first tank removes the hardness, the salt in the brine tank is there to wash the media in the first tank, and goes down the drain. If you have a taste and odor problem, perhaps a carbon filter will take care of it (placed after the softener).
Regardless, any water treatment person can test it for you. Water tests are free. They are trying to sell you the equipment.
If you don't want to fix all the water in your house, you can likely put in an undersink system for your drinking water.
Of course, there's always bottled water.