You know what you can do? You can do a halfy and still have fish that like sand substrate, depeding on the type. Scoot the gravel over on one half of the tank and block it off. You can buy dividers to keep it there, mostly, and still get some that like sand more. Though Cichlids like to redecorate, so you may find things bounced around.
Just don't go for any too big, or too large of a group. In a 29 gallon, I'd suggest either a pair of German Blue rams(these guys prefer sand substrate and like to sift, but it's not a MUST for the full tank, a halfy would be perfect), or a male and two females, or three females if you don't want to risk breeding or accidents with aggression...(they're just as pretty as the boys, some prettier), and six Cardinal Tetras.