Will you share us with the pictures? so maybe we will give you better suggestions...
Looks a bit squashed but you get the gist. There are 3 grasses to come up behind the bird bath and 2 others on the way in the empty patch. What do you think? You can see I'm rather a novice at this but keen to learn!
You might like to search for prairie planting schemes - they usually mix grasses and bright perennials.
grasses are lovely, Rudbeckia would be good, there's a range of heights and colours, also Alliums could go in among the grasses.
Forgot to say - I think your garden looks lovely.
Thank you both for your interest and your comments - I'm on the case!
adding to those suggested, a plant I like to combine with grasses is Helenium, the usual one found in garden centres is 'Moerheim Beauty'. It has a long flowering period from mid summer and is usually a deep orange/red in colour. It can be planted now as small container plants found in the perennial section and they will flower freely in the first year and perennial thereafter.
I love these plants. Have a look and see what you think, as they are easy to plant and dot around the grasses with such startling colour.
I would suggest, rudbeckia goldsturm, vebenna bonariensis, and any of the echinacea family,or to add a twist, crocosmia's, or heleniums...
I love your garden! Can I add to the above excellent lists? Achillias, some lovely colours about these days. And Scabiosa, again, some fab cultivars available in several different heights and colours. Lastly, Knautia, which is similar to a Scabious, available in a bigger colour range now. All of these are 'airy' plants which will compliment, but not dominate your grasses. They all have pretty good seedheads that stand the Winter well. Have a google!