i can think of 3 good choices:
1. albino bristlenose plec - these only grow to about 4 inches unlike the regular bn plec, which can get to 6 inches. they'll suck the paint off your fake ornaments though, so only natural decor for these
2. otos - these grow to 1.5-2 inches. you'll need to get 4-6 of them for a 29 gal, as they like to be in groups. they're also safe with fake ornaments.
3. freshwater nerite snails - stay small and won't reproduce easily. you'll need a tight tank cover to prevent escapees.