I'm agree with Dove, please take in to account that whatever you plant may make your garden shady, or it might also block the sun from your neighbours garden! Beautiful day here in Kent but even with a 6 foot fence my neighbours still feel the need to have another six/seven foot of overgrown, unpruned bushes meaning only one side of my garden gets the sun. Just a thought!
I think any of the ornamental trees for a small garden would be fine - flowering cherry, crab apple, rowan, amelanchier - even a multi stemmed Himalayan birch. Have a look on the rhs website https://www.rhs.org.uk/advice/profile?PID=117
'Optimism is the faith that leads to achievement' - Helen Keller
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https://www.rhs.org.uk/advice/profile?PID=117