Are you thinking of living, growing moss Aimeehammy?
You can use sphagnum moss but you need to freeze it or bake it or both to remove any insects, eggs or bacteria before putting it in the cage, it's not advisable to have any living plants in the cage as plants need both moisture & light neither of which you want in the cage & too much moisture can lead to a humid environment which will then lead to the growth of moulds & an increase in bacteria so not a healthy set up for a ham.
If you want a natural look the go for things like safe woods & cork, you can also use things like dry millet/flax/dari sprays which look nice, you can grow plants for hams to eat (things like oats, barley, millet & some of their other foods, usually grown in a shallow saucer with chinchilla sand) but only put them in the cage for short periods, they're never left in the cage more than overnight & you need to monitor how much your ham eats even then.
As for substrates you can use megazorb if you want something that looks fairly natural but it's very dusty & smells odd! Carefresh natural, again dusty & smells weird or at least it did when I last used it, quite a long time ago now.
Hemp is a good alternative but not that soft, I use
Fitch with
Hugro hemp mixed in, Zooplus also do Hemparade which is more economical than Hugro but I found it a bit sharp.
You can add other things on top of the main substrate like hay & safe flowers for a more natural look too, if you use hay it needs to go in the freezer for a minimum of 48hrs, a week is best, in case of mites then you need to go through it very carefully & remove any sharp pieces that could damage pouches.
Natural looking set ups can be really lovely but do take a fair bit of work & research to get right & keep safe!