I use growmoore multipurpose soil mate. Cheap soil at £25 for 120 ltr.
Over the past two years I have experimented with making a mix soil with added amendment but find that adding the likes of bat shit and chicken shit can cause problems early on. I now just use soil from the bag with nothing added and only water with formulex. I still have loads of miricalgrow granules to use so I add that at the start of flowering with no negative effect.
I'm theory and practical application all you need is a bag of soil and a bottle of formulex
cheep as chips mate.