Advice on Tree for North Facing Wall

I have a Pyracantha against a north facing wall which also has a west wall running along one side of it restricting light even more. It will grow beyond 12' if you let it but I keep mine to about 10' high by about 4' wide. But it is not called the Firethorn for nothing and will keep out stray cats [or neighbours!]. It all depends on how "solid" a barrier you want and whether or not you want a thorny barrier or a "soft" one. Softer Shrubs you might consider are Acuba - 7' to 10', Ceanothus will only get up to 7' but is a nice shrub, Some varieties of Cornus get up to 12', the Decaisnea [Blue Bean] is unusual but there are two in my neighbourhood and grow to 10' to 12', Dipelta [not common but a nice plant, easy to grow] which will get to 12', Elaegnus [varieties with green and gold leaves] easy to grow and will get to 12', Euonymus is a nice shrub with deciduous varieties reaching up to 20' [but it does like some sun], Forsythia Spectablis will grow to 8'to 9', Sea Buckthorn [spiny] will reach 20' and is very hardy, certain types of Prunus are possibly woRth considering. The trouble is trying to balance the height you require to clear a 6' fence, a north facing site which might be exposed to cold winds, and whether or not you want a spiny or soft shrub. Good luck!!