I wouldnt worry too much about sodium. A lot of people, myself included have no troubles with softened water. You will, probably, have to use a GH booster to remineralize the water somewhat if you're trying to grow plants.
BTW, baking soda raises KH which you probably have a lot of already. A softener doesnt remove KH, it just removes GH. I would forget about adding baking soda and instead invest in GH & KH test kits.