Is that soil sterile? Does it have macronutrients?
If you bought a soil with nutes/ferts in it then you could just add peat to it also. I use formula Schultz Orchid Mix 70%, because it has excellent drainage,
20% perlite and 10% peat moss...I spread my moss on the top, to hold water there a little longer, because of the excellent drainage characteristics of Orchid Mix...
some people say to mix soil and perlite 50/50 for drainage...so you see, there are alot of ways, but you need to choose a happy medium for you based on light temps, what base soil you are using, and , of course, strain...goodluck

In the end, it is widely believed that the 3 key ingredients are some type of soil, perlite, and peat moss...