How many, and which type of tropical fish can I comfortably have in a 200 litre tank?

I have a very established, (over a year) 200 litre aquarium. It is heavily planted, with a variety of driftwood and rocks for hiding places. The only inhabitants are five neon tetras.

I would really appreciate some advice on what type of fish I should add to the tank. I do not want to get rid of the neons, so I know I am slightly limited because I wouldn’t want them to be eaten! Any suggestions or advice would be great!