One or More Blue Gouramis Works
I have two Blue Gouramis in a 45 gallon tank with a lot of other fish and they bicker a bit but nothing serious. The keys are 1) Have lots of cover, plants, rocks, driftwood, etc; and 2) Get females! Females have a shorter, rounded dorsal fin and a rounder belly than males (no she does not have roe on board). Males have a longer dorsal fin that comes to a point, and no notable belly bulge. Females are less aggressive than males and so when there is a territorial dispute, it is less impacting. Blue gouramis are more docile than dwarfs or gold gouramis, or pearl gouramis. That's why I went with blues. There will always be one dominant fish and one passive if you put two in a tank together. The larger, dominant female will establish her territory and chase the smaller one out sometimes, but not always. Sometimes they even hang out together in nuetral water. But when the dominant one chases the passive one out of her territory, that's it - She leaves her alone. It's nothing serious and it works as long has there is enough cover. The dominant one takes 2/3 of the tank and leaves 1/3 to the passive blue gourami.
Other fish matter too. Here is what I have in the tank:
5 black neon tetras
3 serpae tetras
3 black skirt tetras
4 white skirt tetras
2 FEMALE blue gouramis
1 male beta
1 pictus catfish
1 clown loach
3 green cory catfish
1 bala shark
1 marble angelfish
Some would argue it is too crowded, but not if there is enough cover for everyone. I'm only violating the "inch of fish per gallon" rule by about 7 inches. The only other conflict I have is a territory dispute between the serpae tetras and the beta fish, but it too is not serious.
Bottom line - You can have more than one blue gourami in a tank if:
1) The tank is large enough
2) There is enough cover
3) They are females!
