Very nice wall. I'd consider planting the woolly thyme between the paver steps since you have it available, but any other low, creeping, full sun groundcover will work - any of the creeping thymes, blue star creeper (can get dieback in winter, so not exactly fully evergreen), leptinella or even Scotch or Irish moss. Both the leptinella and mosses will provide a dense and very cushiony surface on the pavers - great for bare feet :-)

For the top of the wall, I'd consider something a little showier. Sunrose (Helianthemum cultivars) are evergreen, drape nicely and provide a long season of color, Lithodora if you like the intense blue (will also experience some winter dieback), heaths or heathers, dwarf hebes, even prostrate rosemary, although that looks best with a taller wall. Early spring in area nurseries will provide a wide array of blooming "rockery" plants from which to choose, but nearly all are very early season bloomers, so lack color later on. Sedums (stonecrops) and sempervivums (hens and chicks) are great to poke into niches along the face of the wall. Neither they or the groundcovers require any more soil to take hold than what's attached to the roots in their little pots.

There are a lot of really nice mosses that grow very nicely between small spaces and stay green year round. You can hardly go wrong with just about any groundcover, but in your area, I wouldn't get anything that has to have too much sun. Good luck and enjoy.