You could always continue the edible theme. Lingonberries, Vaccinium vitis-idaea, are often sold as a groundcover and will happily share the same planting conditions as the blueberries. Makes a killer jam or syrup. Alpine strawberry, Fragaria vesca, is another possibility. Less aggressively spreading than the more common beach strawberry, they also produce tiny and very tasty fruit (costs a fortune if found at places like Central Market or PCC!!), aka. fraises des bois.

Gardengal:

Do these ground covers work with Gooseberries & Current (red/black & white)?

They should. All prefer similar fertile, well-draining and acidic soils and are well-suited to our climate.

Another possibility is Rubus calycinoides or Taiwan creeper/ornamental raspberry. One of my favorites of any groundcover and it also produces a very tasty yellow-orange berry. Of the 3 GC's mentioned here, it is easily the most robust and potentially aggressive. But by far the best GC I've encountered for weed suppression.

IME the Fragaria isn't dense enough to suppress weeds, and conversely the Rubus is too big for the spot. The lingonberry is a nice idea and should go well with the apples.

Dan

Yeah, you're right, Dan - 4' is a little skimpy for the rubus. Still a great groundcover in the right situation, tho.

I planted some Rubus calycinoides a few years ago. It spread fast, and after a few years, got pretty dense and kept the weeds out. I eventually removed it because it was too aggressive where it was located and started to over run large rocks and small plants. In a larger, less delicate area, it would have been just fine.
Mike