some of the slower growing bamboos might fit the bill. especially if grown in large pots then they wont take over. Then there are other perennial grasses like miscanthus that might fit the bill.

Depends what's in front of the low wall, soil or paving, and if soil, how big an area from front to back. If its big enough, say 4 feet of soil out from the wall, then evergreen shrubs like Euonymus japonica, or Euonymus aureopictus, Berberis darwinii and Photinia spring to mind. Those mentioned which get bigger than you want can be clipped or trimmed regularly. Other choices depend on whether the area is in total shade, full sun, or half and half, and where you are in the country in terms of winter coldness.
If its paving, bamboo in pots 18 inches deep and 12 inches wide will do the trick.

Thanks for your help.

how about some trellis on the wall that you can make to size or probably buy about the right size and grow a fast climber or 2 up it .