Tree/plant ideas for privacy in small garden

Hello,

I don't know if it's possible but I have a small court yard terrace garden and am looking at planting a small tree/ tall plant in a raised bed at the back of the garden where a buddleia used to be planted. I am hoping to find something that will give some privacy from the opposing second floor window that looks on to the garden. It will be placed close to a large old red brick wall and I am hoping to find something where the roots are likely to cause as little damage as possible. 

I like more contemporary planting (grasses, herbs, lavender etc.) and would prefer something that has green foliage and no blossom (although would possibly consider white blossom).  I love silver birches but they are probably too big. 

I would really appreciate any advise as I am a novice gardener. 

Thank you,

Ali