Suggestions Please

Lupins! They flower before the delphiniums, as do foxgloves.
Tall verbena, and if sunny spot, red hot pokers and hardy fuschia.

Ground cover, you can’t beat aubretia and helianthemum and saxifrage, also thrift and small sedums.
Think about middle ground plants though as well, in between these two layers.

At the back, try phlox, anthemis, helenium, campanula, hollyhocks, hardy chrysanthemums, asters and veronica.
At the front, pinks, scabious, penstemon, bearded irises, herbaceous geranium (cranesbill), poppies, catmint (nepeta).

Not the giant catmint though, it’s a thug! Definitely scabious, they flower for months on end.

Tall ones: delphiniums, penstemon, lupins, rudbekia, foxgloves, eryngium, campanula, crocosmia, Echinacea, lillies and red hot pokers.
Shorter ones: pinks, leucanthemum (lovely white flowers that last ages), dianthus, myositis, doronicum and double begonias.
To drift between the 2, plant geums and love-in-a-mist

Lovely selection Chewbacca (apart from the red hot pokers which I don’t like) and some good ideas for my new bed - thankyou!

Tall one- Monbretia Lucifer. Striking orange blooms on long stems with sword like leaves. Comes up every year and thickens every year. Dies down in winter.

For low cover can’t beat various hostas.

Someone on here recommended the hardy geranium Rozanne and I bought one - it's lovely. Mine's at the front f the border but it could go in the middle depending on what height your front plants will be.
Penstemons are usually long flowering.

I have lost delphiniums, hollyhocks, lupins, helenium, rudbekia, aubretia all planted in this garden, whether to slugs or that they did not like the soil I don't know.

So I would advise checking your soil and perhaps adding compost and/or manure for better results.

Sedum seem to grow well as do Lenten roses.

Losing my delphiniums would break my heart Callistemon! I brought several of them from my little cottage garden, which had beautiful, free drawing Liam, to this house which has heavy blue clay. I wasn't optimistic thatbthey survive. But they've done better than ever, much taller bushier and far more flower heads on. The only thing I've struggled with is the peonies; they're very unhappy .

Just another idea clementine, if you have a boundary wall, fence or hedge alongside your flower beds, how about planting some clematis? You'd have virtually care free planting height with a beautiful choice of flowers for different times of the year May - late August.

I have verbena bodariensis, catmint which attracts endless bumblebees and is beautiful, I have just cut mine back to give it a chance to get its energy back. I have mixed in tall rudbekia laciniata and miscanthus sinensis japanese silver. I have cleared a space for some natural foxgloves digitalis purpurea, slightly N facing cooler position

I hate clematis montana especially grown against my fence by next door, it will eventually try to park itself on top of my fence. I won`t let it, I have seen the weight of it pull a fence down, it gets rampant. The small clematis are a different kettle of fish

slug nematodes will clear the ground of slugs

If you like really tall strong growing vermilion roses I recommend Fred Loads. I have one which I dislike as it is too tall for where is is but is so enshrouded in ivy I can do nothing to stop it growing and flowering big blowsy red trusses.

I don’t think anyone has mentioned Astrantia, or Sanguisorba, a tallish ethereal plant with nodding tassels which can come in a delicate white variety.
Persicaria comes in a small variety, although can spread if not watched.

This year I bought three Sarah Raven Dahlias. They are in a pot outside my patio window and they fill me with so much joy every time I see the,. They are
Happy single kiss
Waltzing Matilda
Schippers bronze

Many of my favourites already mentioned here but I also love Alchemilla Mollis - (Lady's Mantle) The leaves are slightly hairy and dewdrops look amazingly pretty on them in the mornings . The acid green flowers look lovely as cut flowers.

Some of the plants mentioned like foxgloves and Hollyhocks are biennial so you could sow some seeds or buy plants now to flower next year.
Mid to front I would suggest border geraniums, Rozanne being a bushy long flowering one. If you want cottage style poppies in various colours are nice, and Heuchera for the front provide all year round foliage of all imaginable colours.

I started a new bed 2 years ago and crammed it with 'sick bay' garden centre plants including Hydrangeas and most of the above suggestions, underplanted with bulbs including Alliums. I have been very pleased with the results.