Sun Gro Horticulture 1410602.Q08P Black Gold Cactus Mix (8 qt) https://www.amazon.com/dp/B00LZ5NP7O/ref=cm_sw_r_cp_api_glt_fabc_M9FZRZNHNY2N99T92GPT

Black Gold is my jam. Already a mix of perlite, pumice, and some other organic/inorganic media. It’s expensive, however.