any angel will be too small for a 29g even a dwarf imo, their active fish like tangs and need room .i would stay away from grazers as theyll be around your mantis's rock alot.personally i would get a fast moving open water fish ,even if it doesnt have an appetite now it may change later its a predator and its built in to its genes
also stay away from ground fish unless your tank is acrylic because if he goes after a crab or something and misses their strike is strong enough to break your glass
i also have a g.smithi he doesnt move much in the tank but he hunts at night and will open his food menu more as he gets bigger and needs more food
cheers