I wouldn't add any new fish for at least a month after the fish have died. If they are developing dropsy it could be from a dirty tank, (dirty gravel or filter), or they have a nasty internal bacterial infection. If you add a new fish now it could catch the problem and die as well.
Most gouramis should be fine with those fish or a short fin male Betta, but avoid the long fin varieties. You could go for a peaceful South American cichlid like a Geophagus of some sort, or a keyhole cichlid, or a pr of rams or Apistogramma cacatuoides.