How about a japanese maple, or acer,if you want colour? They are very nicely shaped trees, quite slow growing, with glorious foliage in the autumn ranging from yellow, through vivid red to bronze, depending on the variety. A lot are smaller than 12ft, but larger ones are available. I'd recommend a visit to Westonbirt Arboretum in Gloucestershire if its anywhere near you - they're famous for the maples in autumn
Check out Amalankia. It has white flowers in the spring which attract wildlife...insects, not elephants !
Also it then has berries for the birds and in Autumn the leaves go a beautiful red and orange.
You would be hard pressed to find better.
Peter