Having a totally fluid space which allows teams to define their own working environment is not really viable for most organizations so is there "one size" that can fit all?

Well, I think that creating an agile work environment is more related to a change in mindset rather than a change in physical space.

Regarding physical space, the space shouldn't impede proper physical collaboration, meetings, either one to one like in pair programming or in groups to tackle any issue. Another key point: have some good information radiators visible from any point in the workplace so people are aware of anything related to the projects they're working in.

Regarding the mindset, in addition to agile values and principles, there's something that I always do: move from the guilty-one-searching mindset to the solution-searching mindset. When people realize their heads won't get cut when they fail, wonders will never cease.