One Peony will be fine in the middle of the raised beds
as they thrive, take up centre space. The flowers dont last for long though. You might like to plant a Delphinium either side of them for ongoing taller interest.

I would look for miniature Roses, they thrive for years and dont take up much space. I bought one in flower in a pot recently. Planted it out in the garden, its thriving, happy as a lark. Better than buying commercial bush type thorny roses.

I have planted Dwarf Lavender Plants around the edges of my raised beds, about 2' apart as they spread. A different variety in each bed. They dont make much work, are attractive to Bees and Butterflies, provide ongoing summer interest. At the end of the season I cut the flowers off, they are now in my underwear drawer !

As for dealing with clay soil, the best cure is lots of organic matter, and, if the pH is low, a dram of limestone, preferably dolomitic. Roses do like some magnesium, and the calcium helps improve the soil structure.
Unlike the advice of older gardening books, the Master Gardeners in the U.S. don't recommend leaving a layer of gravel at the bottom of the bed, since we have found that any sudden change in soil texture will actually stop drainage. In light of that, my best advice is to refill the beds with conditioned soil by putting a couple of cm in first, and scratching it into the undisturbed soil underneath with a cultivator, to make a transition zone into the native soil. After, fill the bed with conditioned soil, and let it settle with deep watering instead of packing. Also, don't work the soil when it is greasy wet, or you will wind up with bricks instead of soil.

You haven't mentioned aspect, that is, whether the beds get full sun, or at least half a day's sun, or not - most roses like a lot of sun, and in shady situations, may not flower very well and will be more prone to disease. That said, roses like clay soil anyway, so prepare the area by adding composted materials when digging, preferably composted animal manure because roses like that too.

However, you might want to choose taller varieties of roses - they are not good companions for most plants, because the foliage of other plants crowding around the rose stems and leaves encourages fungal infections by reducing air flow, so rust and black spot may well be a real nuisance on the roses. Roses are best planted alone, or just with smaller, ground cover type plants and/or bulbs, but if you choose taller varieties, then the peony won't be crowding out the leaves on the roses, just the bottom part of the stems.

Are your raised beds on a concrete/stone base or does the available soil go down below the level of the surrounding area? Could you say what depth of soil you have ?

Trish you need to reply to the question for us to help you. You can do that by writing under the last reply as if you were making a comment.

My raised beds encourage Bindweed roots. Suppose its because they are warmer. I am forever digging them out with a trowel. Break a bit off and the rest come up next year. Its a never ending battle, but I am getting there
slowly !
Also I found the raised wood surrounds were too close together, they caught on my gardening boots. The ones that have been put in on Monty's new friend's garden are much too close together and his feet are bigger than mine.
There are a lot of them too. Its a mistake which is easy to make.