two big fish won't make the tank look "full", they will make it look like two big fish in a glass box that could use a bit more space. I'm presuming your dimensions are in centimeters, is it 60cm wide or high?
There are limitless options for fish that grow to ~6-8" max that could create a full and interesting aquarium. Scape it with rocks and keep a colony of demasonii and electric yellows and you'll have a great mix of colour and activity. Keep a few smaller central american cichlids like sajica, convict, firemouth etc with a school of something fast and medium sized (congo tetras would be great). Create an amazon biotope with smaller eartheaters like red head tapajos, a school of tetras, some corydoras and smaller loricariid catfish, perhaps some angelfish. Even a mix of smaller oddballs like the smaller growing Polypterus, ctenopoma, butterfly fish, spiny eels etc etc could be kept comfortably in a tank that size (more so if it is 60 wide, not high).