If I have a formulation high in soft oils, I use borax. It is the best thickener I have found, helps with lathering and water softening. I add 3 oz to the dilution water before adding the paste. I also add around 1.5 pounds of water per pound of paste. I usually make 6 pounds of paste so this equates to 144 ounces of distilled water for dilution. This make the most wonderful, thick gel type soaps you've ever encountered. I also add 4.5 oz of citric acid to the dissolved soap to act as a chelating agent. Makes nice, thick, lathering, skin softening liquid soap.
If I have a formulation high in coconut oil, I dilute the paste with 9 oz of water per pound of paste. So six pounds of paste takes 54 oz of distilled water to start, if I get a thick crust on top, I add 9 oz at a time until I get the soap diluted, it remains a nice thick soap. Coconut oil is very soluble and doesn't need as much dilution water as soft oils do.
I've never had to use salt to thicken my soaps.