Can you plant wallflowers and sweet William in the same planter?
They have similar care requirements, and can grow in proximity, given plenty of room.
Here are two articles that will help you with the care of each:
https://www.gardeningknowhow.com/ornamental/flowers/wallflower/growing-wallflower-plants.htm
https://www.gardeningknowhow.com/ornamental/flowers/catchfly-plants/how-to-grow-catchfly-plants.htm