A cordyline for the centre piece, they are really robust. They are a spikey thing not a flowering thing, but give height. Thought I had a picture but I don’t.

Depends the size of flower you prefer as we all have our own taste, Lupins, iris, dwarf dahlias, begonias for bright colours, or small shrub like the Azaleas or even a small Acer, lots of choices,