The best soil materials to use for growing carnivorous plants, in my opinion, is clean, inert, silica sand. No fertilizers. No organics. Nothing that would potential harm or slow the growth of a carnivorous plant such as Venus Flytrap plant.
Here in the US, clean sand is usually available in home products/building stores, and is also available in garden supply stores. A quick way to get the right kind of sand, is to just order from Amazon. And if you have Prime, it arrives in two days. Sweet!
But where ever you purchase your soils, you absolutely have to make sure it is inert and nutrient free.
This product will solve that problem. This clean, coarse sand is very inexpensive and the smallest bag will last you a long, long time. I recommend it.