You'll have to stay very small if you want to fill the entire area in front of the C. adpressus. You could get away with a taller and narrow grass in front of each Yew.

Take a look at the smaller Carex varieties. They don't need full sun, and some can deal well with slightly dry conditions. The variegated ones and yellow-green ones would be set off well by the darker Cotoneasters and Yews.

These are 2-year old Carex oshimensis 'Evergold' They barely reach a foot in height.

You could also look at the various dwarf Pennisetum alopecuroides like 'Piglet,' 'Little Bunny' and 'Little Honey.'

Consider also some low-growing non-grass items for fill and color. Dianthus deltoides 'Arctic Fire' is a nice spreader, as is Delosperma cooperii.

Thanks donn!I like the idea of the Carex and the dwarf Pennisetums are also a good option. When we first bought this house there was an old, very dark red, coral-bells growing here - it loves the hot sun. I moved it and think I will bring it back dividing it enough to make a contrasting row for the grasses. Thanks again for your response.
D