You are confusing pelargoniums - not hardy and from South Africa - with native hardy geraniums. 2 different species with a similar seed pod and flower form so when they first arrived in the UK people thought they were also geraniums.
Hardy geraniums will provide ground cover. If you go for macrorhizum forms they will be in flower - white, pale pink or deeper pink forms available - before the roses and the foliage will be scented and go red in winter for added interest. Other forms such as Rozanne will grow taller and flower later and longer and give you blue flowers to contrast with your roses. Hundreds of geraniums out there so go see what's good for you.
Oh! Thanks, this feels a little confusing.
If I ask someone at a garden centre I assume they will be able to point me in the right direction.
@lister_lizard Not necessarily as many staff won't be horticulturally trained. Go online and look at hardy geranium varieties for colour, size, position - some like sun and some do shade and some do partial sun/shade.
If I worried about plants being poisonous to cats I would have a very dull garden. Cats are far too intelligent to eat plants. The only plant they show any interest in is nepeta, that gets shredded in days so I actually grow it in a hanging basket. I would be slightly wary of Lily pollen but otherwise don’t worry .
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This is a good place to start - https://www.rhs.org.uk/plants/articles/graham-rice/perennials-and-bulbs/10-hardy-geraniums and then make a list of the ones you like and see if you can find them in your local GC or can order them online.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.