This custom height quality cactus mix is the best mix you will be able to buy or prob make yourself.  I use a very high quality balanced and neutral coco coir ( balanced amount of coir to fiber ratio) , mixed with perlite , giant perlite , some charcoal, and sometimes fir bark  , also the coir is treated with wetting agent so it will never dry out and be hard to water it down afterwards. This will also come with a small bag of fertilizer ( enough to use on a few plants ( commercial slow release granular fertilizer that I use also) .