@filiz Providing that you don’t have many more thins in your formula, you could replace your c12-13 alkyl lactate with either Versathix or Crothix Liquid (both by Croda). They help increase viscosity on very hard to thicken systems, using low amounts. As long as you don’t have anything to suspend like mica or silicones, you’d be fine.
@chemistry8303 Cetyl alcohol forms a lamellar gel with surfactants, helping thickening a bit while cooling. PEG-150 distearate on the other hand due to its high ethoxylation, interacts with the polar head of surfactants in micelles as a non ionic (as you might have seen, non ionic ethoxylated surfactants don’t give much viscosity when combined with anionics), that’s why Glycol distearate is preferred for creamy shampoos.
There are many reason to be confused, your idea is correct when i use Disodium laureth solfosuccinate as anionic surfactant but It depends on which anionic surfactant i use, I changed my mind when i used Sodium Laureth Sulfate as anionic surfactant, It became thickened as much as it could.