Lyn, my suggestion would be to go in the complete different direction and investigate pond plants, in particular those that can grow in the edge zone and that doesn't need to be submerged in water. They would love the extra water and there should be plenty that would also love full sun. Unfortunately I wouldn't be of any help with specific plant choices being located in Sweden, but it shouldn't be a big problem finding some. Now if you think that the bed would be too dry at times for pond plants, (perhaps there is still some drainage?), then I'd use a pond liner, just to keep the water in and fill the whole thing back with soil. Clay soil should be suitable for many pond plants.
