For height:Calamagrostis Karl Foerster, very graceful, lovely movement in the wind, and is narrow and doesn't take up much space.Medium height:Miscanthus Ferner Osten is one of the smaller ones, only about 2-3 feet tall.Anemanthele lessoniana, arching and graceful, lovely orangey tonesLow growing:Ophiopogon nigrescens, although it's a bit of a marmite plantUncinia rubra/incinata, nice brown/red colouringCarex oshimensis Everillo, bright acid green foliage, does better in shadeHordeum jubatum, not a grass (it's Foxtail Barley), but would look great in a cottage style garden. It's an annual, quick and easy to grow from seed.Be aware that Sedges prefer much more moist soil than most grasses.
Amenanthele lessoniana is evergreen and does better with a little shade. Short-lived but self seeds so you can place young plants wherever suits.Calamgrostis brachytricha - often seen in Piet Oudolf schemes. Actually, calamagrostis in general as they have a graceful (though fulsome) habit as opposed to the bolt upright form some grasses have.Stipa pseudoichu and it's fine and feathery, takes almost no room at the base and wafts above other plants. If happy, it self seeds.
+1 for Luzula nivea.Sesleria are good, they are at most a couple of feet in height and spread, look good well into winter (semi-evergreen), can take being cut back and divided, and have nice flower spikes. S. autumnalis has limey green foliage and flowers in late summer, S. nitida has slightly bluish foliage and flowers in spring. Neither are massively showy in their own right really, but fit in well with perennial planting.
You're going to need a bigger garden Lesley