It would be difficult to find a bush that blooms all summer. You might look at a mix of bushes that bloom at different times to give you color all season. There are dwarf crepe myrtles, to start with. Knockout roses will give you a pretty good bloom, they should cycle several times.

The only shrub I can think of that will bloom all summer is Lantana. There are some cold hardy types such as 'Miss Huff' and others.

Salvia greggii blooms on and off from spring to fall, more often with regular moisture.

Russian Sage blooms in spring and the blooms stay on the plant a long time then there is a second flush of deep purple when the weather cools down. The blue/grey foliage is nice.

You could add Silver King artemisia and do a grouping of all these plants. Add some nice ornamental grasses and you'd have a tough border with much interest and color needing little supplemental water which can take 100+ temps in hot southern exposure sun.

Another good choice is Cenizo also called Texas Sage or Barometer Bush. It blooms whenever it rains. TLC sells them here in OKC and there are smaller sizes, some get taller than what you indicated.

One very pretty grass is Nassella tenuissima (threadgrass). It would make a lovely addition, I've seen it planted in medians with Russian Sage and its a gorgeous combination.

Hesperaloe (Red Yucca) blooms in spring with all asparagus-like stems topped with bright red blooms and the blooms stay on the plant all summer long, visited by hummingbirds. Its called red yucca but its not a yucca, its rather grasslike when mature. It looks great planted in groups and goes very well with the plants I listed.

Autumn Sage is my favorite! I've instructed my granddaughter to bury me in the backyard and plant this on top! Makes me happy just to see this shrub!

I was thinking dwarf crepe myrtle too. Another idea might be to plant some ornamental grasses and plant some kind of long-blooming ground cover around them, like ice plant.

Oh, Autumn sage is good! I have several of them.