Southfacing won't be great for a magnolia, they like a bit of shade. What about Arbutus - A. menziesii prefers acid soil, but the other two don't mind. The commonest one is A. unedo, but all need a sheltered position (southfacing) out of cold winds in winter.
Otherwise, if you don't mind deciduous, consider Amelanchier varieties - blossom in spring, a purple tint to the leaves when they first appear, berries or fruits in autumn, good autumn leaf colour.

Thank you so much I am looking up the varieties now. Really helpful and thoughtful advice.

A south-facing wall in Cornwall, most gardeners would die to have a garden situation like that. Now how about Cytisus Battandieri, the Pineapple Broom, a large, evergreen shrub with silver-green leaves and yellow pineapple-scented flowers. You could have Carpenteria Californica Ladhams Variety, evergreen with large white scented flowers with yellow stamens. If you're hungry, then why not peaches, nectarines, apricots or figs? Albizia julibrissin, from Persia east to China and Korea. It is also widely known as Persian silk tree would be interesting.

Magnolia grandiflora will take quite dry conditions and is often grown against a wall. It is evergreen, flowers for about three months in the summer and the flowers have a lemony fragrance

Thank you both, we have a Magnolia Gradiflora in the courtyard but I love the Carpenteria Californica it looks beautiful, we were thinking of a Ceanothius arboreus. Sadly I think the silk tree would be too big.
Thanks again and will post what we decide on. It is a front garden so not really suitable for fruit.