There is no right potting mix for Paphs or any other orchids. I find you have to try different ones to find out what works best for you. Start out with a good commerical mix and try it. Watch you watering. I use a mix I make myself fron coir, charcoal and shredded Styrofoam I find this works for me. It drains well but holds the moisture in. You have to make sure that you rinse the coir very well.
The web site repotme.com has a good paphiopedilum mix. I have had success with it.
I'll second the repotme.com recommendation. My Paphs took off when I put them in their Paph mix, new growths and bloom spikes all over the place. Plus, their customer service is unbeatable. But again, your mileage may differ, based on your own growing conditions.