try verbena, bacopa, allysum, lobelia. all seem to come in various blues, pinks and white. also if you're looking for a small shrub, there's a cuphea, false heather, that come with white or pink flowers growing to a foot or two. sb daisy, erigeron karvinskianus, has white and pink daisies.

The Chamomile 'Treneague'used for chamomile lawns has no flowers and doesn't mind being watered. It is easy to keep within bounds.

Various forms of Ajuga may provide the cover you're looking for, though some of them can be vigorous.

'Real' geraniums and Erodiums would harmonise with the fairy roses in the white/pink/crimson range as would some of the low-growing Sedums.

I'd be cautious about any of the low-growing Euphorbias; they're interesting but they have thuggish habits.

Stachys could be useful as a foil and it's pretty easy to keep under control.

Another possible is creeping rosemary, though it may not be hardy for you. Phlox subulata, variegated Silene. Sisyrinchium graminoides would give a change of texture/form.