Going from moss to bark is the hardest on them. The roots are used to a more damp environment so they don't do well in the dry environment of the bark. It would be best to get some moss and make a mixture of moss and medium size bark. I just repotted a couple of orchids yesterday that were packed solid in moss. It took an hour each to pick all the degraded moss out of the mass of roots. I repotted them in a 50/50 mixture of moss and perlite to help keep the mixture light and airy. If I had put them into straight bark (which is what they actually should be potted in) they would dehydrate and probably die.