Hi Gary,
I would go for a surface dwelling killifish. What should suit the tank would be a group of Epiplatys dageti or Pseudoepiplatys annulatus both do not grow too big and love to 'hug' the surface.
Otherwise Aphyosemion striatum will also be suitable. And there should be no problems identifying females of australe and striatum. Also biateniatum or bivittatum of sorts will also work.
Obviously I am giving you examples of what I've tried and worked for me. But since the temperament of individual fish vary and the set-ups as well, you should monitor your fish carefully after new introductions into your tank even if it is just another pair of australe.
If you are are not familiar with some of the fish I suggested. Just google the names so that you can see what they look like. And than read up on them as much as possible before you make up your mind.
Quite often though you'll be limited with what is available locally.
Hope this helps,
Bookmarks