Need to replace what I think is box
I have a small shrub in the front garden which I think has a problem. Its suddenly gone bare in patches and I'm thinking of replacing it but not sure what with. I would quite like a small tree but I'm worried about the roots because the garden is raised from the footpath behind a wall which is very old and I'm concerned the roots may damage it. Ive attached a couple of photos which show the shrub in better days - its the yellow clipped pyramid one.
Any ideas would be gratefully received.