need a perennial to compliment my garden...

[Haesuse]

So, in front of my house I have a 12x4' landscaped section.

right now, it has 3 photina red robins in the background, all around 5 feet tall, and a little scraggly. in front of those are 4 nandina firepowers.

in front of that, is nothing. just some landscaping stones. I'd rather not go for monkey grass. but I do want something in the foreground, that doesn't get large enough to ever challenge the nandinas for eye-space. I'm in zone 7b (a very hot 7b), and definitely want it to be a perennial. flowers are unnecessary, but I'd consider them.


any thoughts?