Which is more important to your quality of life - central heating, or indoor plumbing?

Germany has all three. I’m not sure what your point is.

I asked which was more important - i.e. what's your weighting of these?

It is irrelevant, if both are available as base package.

I guess you want to point out that choices are subjective.

That subjectivity is relevant within their classes (air—food-water, security-health-plumbing-heating, smartphone-car-vacation, yaht-designerBrands) Definitely there will be one person who choses to die, just to get latest smartphone, but most people will not.

These classes get less clear/useful as you go up, but most people will agree on the basics.

Tangent: it is important for me personally for my neighbour to have the basics (and more), as that increases my basics like security, sanitary conditions.

GDP is an objective metric, while quality of life is subjective and is inevitably based on arbitrary weightings by the people trying to calculate it.