The default "CP mix" that works for the majority of carnivorous plants is an equal mix of Sphagnum peat and coarse sand. That is easy to say but equal in what way? And do certain plants want it equal one way and others equal another way? It depends.
In North America, sphagnum peat is a commodity product and sold in bags and bales at every garden supply store and big box retailer. There are many brands and I do not think there is any difference between them as long as you make sure it is Canadian sphagnum peat and there is no fertilizer added. In the EU you want to make sure it is German sphagnum peat. Beware of buying any planting medium for carnivores from companies that specialize in fertilizer. It may not be obvious on the bag that they adulterated the peat with fertilizer or other additives such as lime. Also avoid sedge peat mined in the USA and any kind of forest humus.
Most of the sphagnum peat mined and sold is intended for garden soil improvement. For that use quality does not matter too much. Some bales you buy are full of stems and other "trash". Pick out the trash, sift it, or if there is too much trash use that bale in your garden and try to find a different brand until that lot is sold. The quality from any given brand changes from lot to lot if not bag to bag. The small expensive bags of peat moss are probably the same material only fluffed and maybe sieved. They are not worth the extra cost.
Many growers wash their peat to remove nutrients and spores to reduce problems with moss, cyanobacteria, liverworts, ferns and other organisms found naturally in peat. The trade off here is many carnivores appreciate the nutrients in the straight peat but the moss and cyanobacteria in unwashed peat can overgrow seedlings. Washing will also help to decrease the salt in peat. Some brands of peat can have levels of salt that are toxic to carnivores. Please see Rinsing Peat Moss and Sand (growsundews.com) if you are starting seeds or otherwise having problems with unwanted organisms in your soil.
For sand you want a sharp silica or quartz sand with grain sizes in the 1.5 to 2 mm range. The purpose of the sand is to is to open up the soil and help keep it from becoming too soggy. Larger grain sizes are OK but smaller ones can produce a hard compact mass that roots have difficulty penetrating.
I recommend #14 sand blasting sand but #12 and #16 are OK if you can only find them. I am not sure if "sand blasting sand" is the official name. That is what I ask for although it does not say "sand blasting sand" on the bag. What the bag says is washed and sieved (graded) sand. It is available at building materials suppliers that specialize in sand, gravel, rocks, and other hard things like pavers. Try to find a brand that is quartz sand and is not beach sand. If you can not get washed and graded sand you can sieve and wash builders or plaster sand. Do NOT use play sand, plaster sand, or builders sand straight. Pool filter sand is too fine. The fine particles will make the soil mix like concrete. You are better off not using sand at all if you can not get the right sand.
Perlite is a good alternative to sand but it has drawbacks. In some areas it is hard to find perlite that is not salty. Perlite dust is dangerous to your health causing lung problems. During manufacturing and packaging perlite is always kept damp to keep down the dust. They can spray on any old nasty water for dust control and the original source material may also have been salty. I always keep perlite damp and wash it before use. To wash the perlite I put it in a bucket with water and only use the material that floats. I also use it only for plants that will be outside and get rained on to minimize salt buildup. In the past I have gotten perlite that was deadly to the more sensitive carnivores. What I use now comes in bags bigger than a peat bale and is OK. Do not buy perlite from brands that specialize in fertilizers since they may add fertilizer.
You should always keep your planting materials damp. It is easier to measure and mix and it is safer for yourself. I mix the soil with a large kitchen scoop in a large bucket. In the past I used boiling water to rehydrate peat. Someday I might do an experiment to see if it makes a difference. Peat does absorb the boiling water quicker, presumably because of the steam.
When I say a one-to-one mix of ingredients I generally mean it looks to me like it is one-to-one when I am done mixing and ready to use it. Depending on how fluffed the peat may be it might take three scoops of peat to one scoop of sand or perlite to get a mix that looks like one-to-one. For some plants that normally grow in very wet peaty locations in nature I use a peatier mix, for others that grow in sand or gravel I use a sandier mix. Generally you do not have to duplicate exactly the natural soil conditions. Some plants actually do better in artificial soils than they do in their native soils.
-- John Brittnacher
Perlite. Some people sift it to use smaller pieces for some plants and larger pieces for others.
Peat and sand, the default mix.
#12 or 12 mesh sand blasting sand with metric ruler. The grains are about 2 mm in size. I do not recommend sand finer than #16.
The sand comes in 100 pound bags. They are heavy.