So I bought some popcorn salt so I can have a finer salt to use for the sugar cookies.With the regular table salt I was using, I could always taste grains of salt in the cookies even when I mixed it in with the sugar and butter instead of with the flour. Like the grains are too big to get mixed in! Would I use the same amount of popcorn salt as regular table salt in my mix? Or less popcorn salt because it's a smaller grain . . . I use 1 tsp. in my recipe or regular table salt.
I’m not sure what the conversion would be, but I would add less (maybe 3/4 tsp) since you seem a little sensitive to salt. You could also try using salted butter. If you use salted butter instead of unsalted, you can reduce the salt by 1/4 tsp for every 1/2 cup of butter.
I imagine you'd want to use a touch less, as the finer grains will be more compacted in the measuring spoon (so you'll get more salt by weight with the popcorn salt if you use the same volume measure). But I would probably just do a few trial batches of dough with varying amounts, and do my own taste tests to determine the optimum amount.