I would advise against getting another cichlid. 29g is a small tank and your EBA already knows it is his territory, even though they are very mild, I doubt he wants to share. Other cichlids which can live in a 29 are few and far between.
As far as the schooling fish- avoid barbs, larger rainbowfish, and "nippy" tetras like Buenos aires. Most others will be fine. Glo-light, von rio, cardinal, emperor tetras would be fine. Danio species other than the giant danio, will also be fine. I would stick to 6-8, no need to overstock (your tank is approaching fully-stocked as is)