I would go with baby mysterys, then move them when they get too big for your comfort. Or regular bladder snails. Nerites and ramshorns produce a lot of eggs but could work. Ramshorn with caution because some might eat plants. MTS with low feeding can still produce high numbers, and large adults could uproot small plants theoretically. Rabbit snails would definitely not work they eat plants quicker than any snail I've seen, even my giant apples. Assassin snails would be fine, they stay smaller than MTS, but are purely carnivorous, so would need sinking carnivore pellets. There are more options I cant think of though, but most would probably be burying species like MTS, rabbits, and assassins.