Spotted Raphaels max out around 6" ,same with the Asian Bumblebees Striped Raphaels tend to stop arounf 8-9" for very old individuals, Pictus is a great choice, some of the smaller Synodontis species would work, Hoplo cats rarely top 6" but can reach 8" in some instances. Madtoms are also another option just make sure they are not protected in your area and follow proper quarantine procedures.
Severums are typically peaceful and grow 8-10" and on the smaller side Angelfish would work well, as well as the Aquidens species, most Andinoacara species (except rivulatus in a lot of cases), Bujurquina,..... Discus if you have the right water chemistry, and a school or even just 1 or 2 of Geophagus (warmer) or Gymnogeophagus (if u keep cooler temperatures)also.