Best tree for a mixed border

[Tilkyghg6366]

Any suggestions?

How big do you want it to get?

Amelanchier

Not too big ie not ridiculously enormous.Already got an amelanchier.

Acer, pittosporum or cornus kousa. Flowering cherries are lovely in spring and you could always grow a clematis or rose up it to provide interest later in the year.

Other suggestions -
Prunus serrula (definitely if the sun would light it from behind in the winter).
One of the fancier rowans - huphenses maybe? pink berries last for ages, also have more delicate bluey foliage than native rowans.

Field maple

Cersis canadensis is lovely, or a eucalyptus would be a nice splash of grey-green, and if you choose a dwarf variety (and mine it for foliage for Christmas - that's my intention! ) it'd be doable. Or a crab-apple? I've got a little Japanese cherry called kojo-no-mai that is gorgeous in spring and autumn.

A shrub rather than a tree, but I’m staggered at how wonderful my Corylopsis looks at the moment, festooned with dangly tassels if yellow flowers.

How about a red hawthorn? There's a variety called Paul's Scarlet.