Nearly all easy-to-grow Nepenthes are plants that will eventually get large. N. ventricosa and x "ventrata" will stay moderately compact for a while, but nearly all have the capacity to exceed 10 feet or more in length. The only truly small plants tend to be highlanders or difficult lowlanders, though some hybrids with these may be good choices.
Humidity is an entirely different factor. Again, the easiest plants in this case will eventually get big.