Are you using SLES as a powder or liquid? (I initially assumed liquid, but even as a liquid, this percentage is quite high. I would balance it out a bit more with the decyl glucoside to make the formula more gentle...I understand this may be cost prohibitive)
Essentially you should be able to thin out your current formula with water until it reaches your desired consistency, and then you can test the lather.
Have you taken the pH of your final solution to ensure that the preservatives you've used will be effective in this formulation?
I would recommend signing up for a free account with UL prospector, they have a lot of good formulations. Also, sites like make your own, etc have a lot of good starter formulations.
Here's one I found from PG (#4 seems to be a polyglucoside)
I made soap using synthetic materials as well like SLES.
If you're confused on making a new formula for thinner liquid, just add water and stir until it reach desired consistency. Then adjust your previous formula with additional water.