What should i get fish pro's only?

OK i have a 20 gallon tank with 2 corydora sterbai 2 julie corydoras 2 lemon tetras and a black neon tetra lot of room in my tank not being used I want 2 more fish to complete my habitat i want them to be like the vocal point of the tank My tank has bountiful hiddins with a rock structure and a beast of a filter. I am not afraid to spend 10 bucks a fish for these ones that i want to get