They're all very pretty...they aren't year round, though..so you may want something that is evergreen in there, too.
Butterfly bush comes white/pink/lavender colors I like the purplish/lavender/blue ones the best...they tend to send out spikes of leafy blooms and the flowers are also in spike form and attract of course butterflies!

You can prune them back if they get out of control and keep them a nice sized bushy plant...they grow to be about 4-5 ft tall and maybe 2-3 ft wide...some can grow bushier.
Endless summer hydrangea...not sure about this particular one..I'm more familiear with oakleaf hydrangea and blue nikko (japanese form) with the blue/pink blooms. But a typical hydrangea can grow fairly large (8-10 ft wide and up to 5 feet high...they, too, can be pruned back fairly easily)
don't know lick about cat mint
irises like well-drained fertile soil that stays moist....they go very well next to water elements in a garden. They have beautiful blooms and they are my home state's flower!

Tennessee..
Some of my favorite garden plants....granted I'm in north Alabama..so don't know your zone...
Stells D'oro Daylilies...really any daylillies...the Stella's just tend to bloom most months of the growing season.
Gumpo azaleas...low growing shrub form...pretty foliage and nice blooms
Evergreen tree form plants...broadway cypress, dwarf alberta spruce, mugo pine (birds nest plant), and love the blue weeping alaskan cedar...gets up to 40 feet tall but only 10 feet wide...beautiful...and deodar cedars....little gem magnolia
Deciduous faves....yoshino cherry tree, sago kaku acer palmatum (jap maple with coral bark), dogwood....
Have fun planting...we're working on my backyard all day tomorrow!!!

Tara