Make sure you use a "moisturizing conditioner" to co-wash....The clarifying ones may have some strong natural cleansers in them that work as well as a shampoo. Companies are doing this now since people are 'co-washing' more....The "strengthening" conditioners may have protein which will make the hair stronger, not necessarily softer.....
Its good to clarify before starting a co-washing regimen. I clarify 1-2 times a month with 1 tbsp of ACV mixed in 1L of warm water (let sit 15 minutes)....Or I will use a shampoo with sulfates such as CON....I use CON maybe every other month.....But clarifying from time to time helps....
If that still doesn't help when you co-wash, add a little oil like Castor Oil to it, and let your condish sit for like 30-45 minutes or more....then rinse like 90-95%, leaving some of the diluted condish in the hair.......I did this the other day and 4 days later my hair feels soft and moisturized...I will clarify next wash, since I did it 2 weeks ago....
I'm a mixologist, and I am not averse to cones right now...I minimize them as much as possible during the week....like my last co-wash/DC I mixed VO5 (Moisturizing Condish-pomegranate and grapeseed oil) with ORS Replenishing pack a dollop of Joico Kpax and Castor Oil for 20 hours....washed out, did a light blow-out with a little CHI Silk infusion....4 days later (though my roots reverted from working out) my hair feels moisturized and soft......I wear twists and just took the twists down today, and my hair feels great...I co-wash weekly with VO5....(cone-free)
I havent done anything but add a little castor oil (for thickness) to the scalp once, and some leave in on my ends for protection...I have not re-moisturized at all.....
This takes time, patience, and for some----creativity...