I have tried everything over the years to make my towels soft. First was the fabric softener and dryer sheets, then the baking soda and vinegar. Although I still use the vinegar, they were still scratchy. I searched the internet for solutions and found the answer.
I was doing two things wrong when I washed my towels, first I was putting too many towels in the washer. Second I was drying on too high a heat, set your dryer to medium heat. I have washed my towels twice since and they are a lot softer now, I'm sure on there way to being very soft.
I have tried to do the same thing over the years. One day my doctor told me to use scratchy towels on my skin. He said it was good for blood circulation and also exfoliation. Now I don't worry too much about soft towels.