Just like apistos then! 😂 Those females are like tiny tanks.
The black phantoms would look great in this tank, they'd really bring the drama!So for me I'd try a nice medium ish sized tetra to add interest, with perhaps black phantom tetras my pick. They are a nice size and won't out compete the green neons, they are easy to keep, easy to sex and you get really nice sparring behaviour from the males when they are trying to impress the females. They might be boring to a lots of people but they are very calming to watch.
If this was my tank I would also really consider a group of pygmy cories like Rosie suggested.