Hi dreamer, and welcome to SRC!
Keeping a nano reef tank can have its own challenges. It is less forgivable in terms of swings in water perimeters, so your aim should be to create as stable a condition as possible.
The best type of marine bio filtration would definitely be live rock. The more porous the better. However, in a nano tank, space is a constraint, and to fit in as much bio media as possible, you might want to consider using more compact forms. I would personally recommend Bio Homme. It has to be coupled with mechanical filtration though, as you do not want waste to get trapped in them.
Keeping a low bio load (minimum number of livestock) would be the best option.
You might want to visit Nano-reef.com to read up more about nano reefkeeping. Check out the monthly reef profiles for some inspiration, but more importantly, how they achieve it.
Happy reefing!