Corys can be difficult, but I would be interested in knowing the species you had. Some are more-so than others.
As for other fish, I would normally suggest increasing the rasbora, but here I would not. Eight is a decent number in a 29g, and having another species or two, which probably will mean groups of each, will provide more interest. Of the three frequently-seen Trigonostigma species, T. heteromorpha (the Harlequin) is the largest and tends to do OK with not as many as the other two species are better at.
Depending, corys might be good, a group of 6-7 [might have suggestions when I know which species you had]. Whiptail Catfish or the Red Lizard Whiptail Catfish are hardy and rather more interesting for a substrate fish, while not getting large--just make sure it is the Rineloricaria species in our profiles, there are some similar species that get large and may appear under the same common name which is misleading.
For other upper fish to match the rasbora, some of the quieter tetra can work. Pristella maxillaris, Lemon Tetra, Black Phantom Tetra, Black Neon Tetra come to mind for being different colouration.