I've recently changed from using Fairy Non-bio to Surcare Sensitive because of fragrance allergy, and my towels have become seriously crunchy and cardboardy. I like a slightly rough towel, but when it is so stiff that it doesn't even drape around me and I have fold it like cardboard - it's getting a bit ridiculous.
I don't use fabric conditioner, haven't done so for about 7y, and line dry whenever possible. I don't really want to start tumbling my towels to get them softer.
do you have space for them to dry outside? the movement from the breeze helps softening them. if you use softener they don't absorb the water as well. I give the towels an extra rinse and another spin and then put them in the drier for 15 min before hanging them to dry.
I read somewhere that you shouldn't use fabric softener on towels as it makes them less absorbent. Something to bear in mind. Although I know that goes against your problem of trying to make them soft!