You can get metal peony supports. Or use twiggy cuttings pushed in around the plant before the foliage has emerged very far in the spring.

The foliage stay upright, because it's a tree peony. My herbaceous peonies have foliage that droops. This tree peony has pretty sturdy branches, it's just the stem of the flower that droops. If you look at the leftmost peony, you can see the very short stem curving down.

So stick the twiggy cuttings around the flowers.