My inclination would be to consider a contrasting form, both to flower and leaf, and maybe size. Something spiky? Airy? Waving? Or low, small leafed? But you may have a different overall design in mind. The sedum may read as a color variation of the bobo, at least from a distance. Is this what you want?

Low, evergreen, and small leafed:

one of the frosty foliaged, low growing Dianthus such as pink flowered Firewitch or white flowered Greystone

Veronica “Georgia Blue“ which has blue flowers and green foliage that takes on mahogany hues in winter

grassy looking:

one of the ornamental Sedges such as Carex ‘Banana Boat’ or Carex ‘Ice Dance’.

dwarf iris like ‘Blue Denim’

Bobo is smaller than most paniculatas, and the ones I have seen in gardens flower top down to ground level, so I wouldn’t want any taller or bushier plants very close. I think Matrona is taller than I would want, but perhaps Angelina or Dragons Blood.

How about Purple Fountain Grass

You would likely get some good suggestions on the perennials forum as well since some folks there grow Bobo.

That Hardy Geranium as a companion plant is great idea. I also like- Phlox stolonifera 'Sherwood Purple' (Creeping Phlox) . But thinking Hardy Geranium is even better! Anyway a photo above (not my photo) of "

Phlox stolonifera 'Sherwood Purple' (Creeping Phlox) "

But which ones bloom when BoBo blooms? Not Sherwood purple? Or doesn't it matter?