I put together my own very simple mixes for most of my carnivorous plants, but for my first time growing pings it was very convenient (and likely cheaper for the amount that I needed) to purchase a pre-mixed bag of ping-specific mix from a reliable seller instead of figuring everything out from scratch or attempting to buy a generic "carnivorous plant" mix elsewhere that likely would be more suitable for sundews or fly traps. I received more than enough mix to fill up an 8" succulent bowl and have a reasonable amount left over, and have been growing three different species of pinguicula in it (plus some much more recent additions) with great success for three months. It's effective, well-draining, but retains moisture well enough that watering is only necessary once a week or so.