Prunus Amanogawa

I'd second that...

my rowan is a slender one so that could also be a possibility.

I had two rowans at my old house.......very very slim(sort of vase shape I suppose you would say) they were rowans..Autumn Spires. They were fairly slow growing .In 10 years they only grew to about 12 FT tall and 2 feet or so wide. The autumn leaf colour was spectacular and also had orange berries!!!
They were ideal for planting on a boundary as they didn't have branches that overhung into the neighbour's garden.

P. Amanagowa would be my choice....i have 3 close together and they're superb

Another candidate is amelanchier 'Ballerina'. White flowers and coppery young leaves about now, berries in August that birds adore, and autumn foliage colour as well.

Very tall and very thin and evergreen - Juniper Skyrocket.