i would do the bolivans because they fight but dont kill, i had 2 firemouths in my 35 and they killed eatch other, and you can have 4 bolivans, or 2 bolivans and 2 gold/blue rams
Bolivians would probably work fine. They like soft anf acidic water in the wild but they have been tank raised for quite a while and are pretty adaptable as well as hardy. They are very peaceful and should be house with other peaceful fish. You shouldn't have a problem finding them as they are fairly common in stores since they are hardier than blue rams. They so get a bit bigger than the blues too...4 inches or so.