Planting near boundary

[BlueFlint]

Our very nice neighbours have just completed a single story extension which is quite large and runs along the length of our garden. It's about 1m from a newly installed 6ft fence (we've removed the large Leilani hedge that was previously on that boundary). It's a very nice building but a bit imposing from our side, just because it's so close to our garden. I'd quite like to break up the view a little. I know planting trees probably won't be appropriate because we don't want to cause any damage from roots and it would be challenging to prune them from their side if they overhang too far. Anyone got any smart ideas for what we could plant? There will be a flower bed along that fence on our side which could accommodate shrubs etc.

I would plant a variety of flowering shrubs which would give interest and variety throughout the year. What you plant would depend on which way the border faces and the type of soil, Maybe Hydrangea, Escallonia laevis "Pink Elle", Potentilla, Hypericum "Hidcote" would be suitable.

you could have espalier/ pleached trees if you choose a variety with noninvasive roots.

https://www.pracbrown.co.uk/semi-mature-trees/choose/pleached-espalier/

Climbers that go to the top of the fence, and higher still if the building you want to screen is taller than fence. What about clematis? There are different kinds that flower in spring, summer and late summer, and one or two that are evergreen. They all like their feet in the shade but some sun higher up. There is also a "climbing" fuchsia (not a true climber but can be trained against fence or trellis) called Lady Boothby.
They could go at the back of the shrubs. There are tall shrubs that could help screen as well.

Thank you for the excellent suggestions, several things I hadn't considered! I think we might go with a combination of your ideas. Tricky trying to find the balance between breaking up the building behind, but not planting anything that will cause issues for the neighbours (they really are very nice and we don't want to be a annoying!).

Could you attach some trellis to the fence along the top of it?