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With a 29gal there's not too many choices aside from a few Cory's. With a school that size, the TB's should leave Cory's alone, but there's no guarantees. It's a toss up if they'll ignore the Cory's or bully them.
In larger tanks ... like a 55gal and up ... other bottom dwellers you could look at are Rainbow or Redtail sharks. They can hold their own against TB's. Clown loaches and TB's also get along from what I've read ... though Clown Loaches do get rather large.
Glass catfish can be very delicat amd dont handle changes in the water well, if you get these guys make sure your tank is fully cycled and have some plants as they seem to like to hang around them