Lindsey, how much room are you giving the flowers fronting the cascade of pampas grass leaves? Pampas grass leaves are sawtoothed and as they blow in the breeze will tear up/damage foliage plants leaving them open to bugs,disease or loss of water.
Pampas likes well drained soil on the medium to dry side. Tough competitor for moisture with flowering plants. I know the only thing I've been able to plant closely is yucca but the yucca spines made fall trim of the pampas a dangerous job. Good luck and if you find some plant material that will coexist with pampas please share that here with the rest of us.