I have clay soil too and have a cottage style garden full of perennials. I too have lost a lot along the way, but by trial and error have found some that just romp away and are quite happy with their lot.... Japenese anenomes, foxgloves, euphorbias, delphiniums, aquiligias, forgetmenots, ladies mantle (alchemilla mollis), sedums, geraniums, cat mint, astrantias. So quite a few successful. I do try to throw on and dig in some home made compost and leaf mound every autumn which has improved the soil a bit. I have lots of pots too and dont find perennials very successful in them, although hostas are quite happy in them and they have more protection from slugs than in the ground. I grow lots of bulbs and tubers in my pots, spring bulbs, lillies, agapanthus, dahlias, also fushias. I tend to grow the bulbs in large plastic pots that then get put in glazed blue pots on display when in flower, that way I can keep rotatating pots and keep a show going. Hope that is helpful. Good luck.