These plants are typical wet meadows and like moist soil: Valeriana officinalis, Symphytum, Filipendula ulmaria, Lythrum salicaria, Alium ursinum . They are fairly robust and with a little care should survive Aegopodium. It should be fairly easy to collect seeds in nature end of the summer, a bit earlier for Alium ursinum, or look for a plant shop specialized in indigeneous species. You can also try Ficaria verna by spreading some tubers collected in nature, Alliaria petiolata, whose seeds should be mature soon, but it flowers the second year only.
You can try Dipsacus fullonum and Oenothera biennis for dry land but honestly, looking at your Aegopodium, I would definitely bet on a wet soil.
Check also which birds you do have around. Some feed on seeds, others on insects which should influence your planting.
Do not discard the grasses too fast: they are host plants for the caterpillars of a bunch of butterflies, mostly brown, you will start seeing in early summer