Here is a guide to tell you what makes different styles of cookies: butter or oil, sugar white or brown, baking soda or powder, flour refined or whole wheat.

You would most likely get what you want with granulated sugar and baking powder.

What makes commercial chocolate chip cookies soft is invert sugar. This is a particular class of sugars that have the property of chemically binding water, so that baked goods containing them don’t dry out.

The most readily available form of invert sugar is corn syrup. It doesn’t take much invert sugar in a recipe to get the moistening effect, so cutting back slightly on the regular sugar in a recipe and replacing it with a little corn syrup will soften up the cookie. Something along the lines of 10% (by weight) of total sugar should be about right.

Brown sugar instead of white would help.