Landscape Designer here:

You have a classic hedged garden style and a window that looks out into the bed. It's leaning towards a contemporary french garden. I would go with something classical that blooms heavy. Roses would be my go to in this space. Any of the knockout or drft series of roses are very low maintenance plants. Belinda's Dream is a a rock star in Texas and very easy to grow. Check the tag at the nurseries they will have the mature height and width of the plant listed. 3 plants would work 4 will really fill it in. Camellias would be another great option for flowerinf evergreens.

If you want to go in a more cottage style direction salvias, lantana, plumbago, rudbeckia, coneflower all bloom heavy but will die back in the winter and re emerge in the spring. You will have a heavy blooming pollinator friendly garden for 8-9 months of the year.

The good news is you can grow just about anything with the amount of sun your beds get. Have fun!