I guess with any fish I'm taking a chance on their individual personality but I think either of these will do, even a sajica as
J
Joshuakahan
suggested. At the moment I have no idea where to get a deppi or sajica ( I've seen a Sajica once, but neither seem to be common around here). But I'm sure I can find someone around my area or someone who can ship fish from interstate. The puffer isnt really an option since they arent allowed in Aus, so the few that are left are hard to come by and I imagine expensive to boot.
I'm in the same boat, I know this tank would be perfect for a bonsai or like a Blood Parrot but I don't want to get attached to a fish that would be constantly ill/suffer or die quickly. I think I might follow
Ruturaj
's advice and try for a female Red Dragon, upgrading in 2ish years if she tops the 8-9" mark.
They both look pretty good, hopefully you can find a quality male as well. Do you find the female Flowerhorns to be as active as males? I'm thinking a female could be the way to go here.
What does everyone think about the H.Carpintis option?
https://www.monsterfishkeepers.com/forums/threads/h-carpintis-maximum-size.196585/ and
https://www.monsterfishkeepers.com/forums/threads/curious-about-texas.239870/ I found these old threads and I feel like the watered down ones in Aus probably top out at 10" after a year and slow growing through 7-8-9", especially a female.
Thanks for all the info so far guys, please keep it coming

Trinsfish .com has sajicas