I have a weak spot for cushion forming rock garden plants with sessile flowers. Silvery dwarf harebell is one of those plants. Given the right conditions it becomes covered in purple flowers in late June - July. It needs sharp drainage and here in the south where the winters are wet, it's best chance of surviving is on a steep slope so it doesn't sit in water. A mix of sand and 20-30% soil has proved effective with fine gravel on the surface. It needs full sun.