I dont like bark as a medium for epiphytes either, but I still do like them mounted so I grow them on terracotta, designed as little twigs or stems, depending on the size of the stems ( my miniatures are mounted on equally tiny pieces). It has the same functions as terracotta pots, so its able to suck up quite a bit of water in itself and the surface is also a bit rough and has carved in ridges to provide a better surface for the roots to grip on. Im also growing some tropical mosses wich I attach in patches to the media. Unlike Sphagnum, it attaches itself to the media over time as it grows, just like the mounted plants, allowing to remove the threads after some time, wich I really like. It ends up covering the entire media and grows a whole lot slower and finer than sphagnum, lowering the risk of it overgrowing the actual plant. Downside is that these types of moss cant take up nearly as much water as sphagnum, so I have to watch out for moisture even more carefully. I do love sphagnum as a top layer for carnivores tho, like Drosera or Nepenthes, and grow two types of sphagnum, one native to europe for my houseplants and one tropical for my terrarium plants.