Are you in Belmont? Do I know you!!?
I have mixed beds of herbaceous, grasses and shrubs, so that there is something to look at year round.
Light levels in this area are rubbish (I used to live further south, so notice the difference), plus Belmont is fairly high up, so generally a few degress colder. And to be honest, I really struggle to find herbaceious stuff that will thrive. Though having said that with temperatures warming up, I can grow more here now than I could 15 years ago.
Astilbes do well. I like Astilbe 'Fanal' in particular. And had great success with Aconitum nepalus, which everyone mistakes for Delphinium. It is very poisonous though. Also Iris sibirica. Lovely delicate flower though doesn't last long. Heucheras and Tiarellas do OK.
And I do like grasses. Really I rely on Shrubs. Acers to brilliantly here, and I've got a georgeous Cornus controversa 'Variegata'. It's just starting to shape up after we removed a big confier that was getting in it's way. And across the steps I've got a Phormium cookanium 'Cream Delight', and its exactly the same green/cream foliage as the cornus.......a happy accident. They light up the garden on a dull day...... like today.
Oh, and one I'm having a bit too much success with is Chaerophyllum hirsuitum roseum (spelling might not be perfect!). Pink cow parsely, flowers late spring/early summer, and then cut back for ferny folliage. Seeds like mad, a bit like Alchemilla, but its lovely and unusual.
I think for quality perennials, I would go to Crocus, especially if you need a reasonable quantity. They've got a better range than the average Garden Centre, and whilst I wouldn't say they were cheap, they're are no more expensive. Worth having a look. Catforth Gardens near Preston used to be really good for perennials, but I think it closed down? Not sure.
Did you go to the Tatton Show? That's always good for perennials. I was very good this year. Didn't buy one single plant. Because to be honest, I couldn't fit one single plant more into this garden!