Marimos lie flat but they never truly attach to anything. So your best bet would be to spread them out and glue them to mesh/rocks. They grow really slowly. They also tend to collect and show a LOT of debris. They look great in pics but in reality they're a pain in the butt in my experience.
Xmas moss will grow a lot faster but will also be a LOT taller/bushier than marimos. It will only work well as a carpet in a bigger tank IMO. Mini x-mass moss is tall enough to make up the midground in my 3.4 gallon nano.
You could also try fissidens/mini fissidens on mesh.
you should look into fissidens they look really nice but grow slow. and in my opinion, christmas moss is better on drift wood since it kind of grows in sheets. but it still works on rocks. but id suggest taiwan moss as it grows a bit faster and looks about the same.