Rather than spend loadsamoney on tall trees or hedges to provide privacy from overlooking neighbours, which can be objected to by those neighbours, what about erecting screens (of dark mesh high on poles, for example)? In the UK, are there any restrictions on how high such screens can be and how far inside the boundary?
The maximum seems to be what your local authority would permit, so you would need to contact them. But, I don't see any reason it can't be further inside your own garden, if you want it.
Fence panels are restricted to two metres in height, even including trellis on top. I need far higher. Climbing plants don’t create much height, and they are destructive to the panels
Is it that your neighbours can see into your garden from upstairs windows. If so difficult to solve without using some sort of tenting that would block out the sun as well.