I would look in a book with clay recipes specific to the cone you want to fire to.A good one is “The Potter’s Complete Book of Clay and Glazes” by James Chappell
A good earthenware throwing body recipe is
60-local red clay
10-fire clay
10-Kaolin
8-SIO2
10–40-60 mesh grog
2 -Jordan clay
fired to cone 08–04