There really isn't anything you can add to the bar to help with shine. This really is the biggest downfall to me for using shampoo bars. Using a vinegar rinse will help some but what really adds the shine back it to rub a few drops of coconut oil through the hair while its damp.
Shine was the reason I made a synded bar instead of shampoo bar, the last one I used for a year and somehow it stopped my hair loss. Then I switched to synded bar using baby safe ingredients. Shine is back and so far so good not hair loss. (Iam knocking unpainted wood right now) )
Yes, a synded is synthetic, it uses detergents instead of natural soap. Think of them as regular shampoo but in bar form.
Increasing the SF in your shampoo bars will not help with shine, it will just leave a sticky residue in the hair. You might try increasing the cleansing number a bit, that helped with my hair. I started adding 5% coconut and the resulting bars didn't have as much residue.
Speaking of hair loss: about 10 years ago I started having heavy hair loss and at that time I know stress is one of the reason. without thinking much about it I started using coconut oil. I applied coconut oil and left it on over night and wash it every morning. to manage stress I started doing TM meditation for 30 minutes a day. then I started using pranayama breathing exercise. hair loss stopped after about 2 weeks of doing all this. well at that time I didn't know I could make my own soap. by only using a soap hair loss stopped thats very impressive. can you share the recipe ? I know caster oil and coconut oil are good for hair loss. to apply directly and leave it on for half day or as long as possible. stress is one of major issue for hair loss.