I have a 30 years old planifolia and used almost all that time half compost, half bark and bits of expanded polystyrene. It works fine for about 4-5 years then you should repot as you can be exposed to a winter watering accident with a pot all composted, a vanilla not doing much and too much water as it needs less when not conquering the world.
This year, I've changed the medium and it's now half "orchid terrestrial compost that kills phals sold in garden centers" that is a mix of half rotten bark, coco, compost, fine for cymbidiums, 4/10th of cork bits, 1/10th perlite. I've added good bark on top just to cover. It's a very springy medium, like a forest soil. And the Vanilla just thrives.
I've never understood those trying to go all epiphyte with vanillas as they LOVE water when growing (that is 9-10 months a year in Paris), humidity all year long and grow from the ground in real life. They should be ok with (semi)hydroponics but I've never met an example save here.
A word on the pot and supporting structure. I use like at least a friend with a vanilla, a pot with a water reserve, it's does wonders in Europe. And we both have a bamboo tripod to support (friend's one broke even once).
Hope this helps.