I grow N. lowii (and almost all my other neps too) in spahgnum mixed with about 25-50%small grade orchid bark with a dash of charcoal thrown in since the plant won't be repotted/moved for a couple years it helps keep the soil fresher longer.
I vary the amount of orchid bark depending upon the habitat of the plant. Epiphytes who like to get noticably drier soil between waterings (N. lowii, inermis, macrophylla, macfarlanei, hamata, etc) get the most bark in their mix.
When I pot up things like my bicals, ampullarias, mirabilis, etc. I put in much less bark but still enough to keep the mix open and allow for slight air movement through the soil. For swamp growing lowlanders and other forest floor dwelling plants I add a few handfulls of a product called Oak Leaf Mould. This is basically sterilized crushed leaves you'll find it by the seedling mixes and maybe orchid bark. This adds an acidic element to the soil mix but it will not stay too wet for very long and it does not compact like Peat does in my grow chambers.