Flower bed ideas

I’ve got this part of my garden to play with. After planting a couple of small/medium sized trees on the opposite side, I was thinking of planting a flower bed here after covering the grass with cardboard but have no idea where to start and what might look good here. It’s partial shade and clay soil but does get some full sun late in the afternoon, so I was thinking of something like a clematis on the fence.

Any suggestions are appreciated!