How low growing? Lantana gets up to 3' but will come back year after year and loves heat. Lavender does well too. Dianthus of various types should do quite well and come back each year. Verbena comes in various colors and is quite beautiful with its velvety leaves and petals. Gazania blooms nicely and comes back, as does mealy blue sage.
No matter what you choose, put the cost of mulch in your budget. It will help the plants survive between waterings because it helps deter evaporation, it will regulate the temperature around the plants' roots keeping them cooler in summer and warmer in winter. And a bottle of seaweed and a foliar sprayer to give them a weekly spritz will keep them happy and blooming.
Hope that helps!
Kathe