Acer palmatum var. dissectum 'Garnet' is a small maple with deeply dissected leaves that are a deep red. Ultimate height about 1.5m and 2.5m spread according to the RHS website. Most other maples grow to about 4m (about 13ft) ultimately. If you are on chalky soils though, a maple won't like it and won't grow well.

The acer will not particularly like being in the shade all day though and if the site is windy the leaves will get burnt and torn.

Granted, Moon Grower but I'm working on the principle that the only part of the garden in permanent shade is close to the house, the other end of the garden and one side will usually get sun at some time of the day, whatever the season (weather permitting). I suggested an acer because I think their leaf colouring is quite spectacular

If you don't mind an eventual height of 10 feet, Amelanchier 'Ballerina' is a good value shrub/tree - blossom in spring, new leaves tinged purple, bright red leaves in autumn, interesting shape when bare, having more than one main stem usually.

Ditto Bamboo.

I was going to suggest Amelanchier too. then you could consider Rowan too.

the white rowan Sorbus cashmeriana could look wonderful and in 15 years our is still only 7 foot

yes that is a beautiful one mg. good suggestion :o)