One idea that springs to mind is iron filings forming field line patterns, but I don't think this is ideal.
I would say the most 'natural' inductor is just a single piece of wire, but you can't have your cake an eat it too.
If you want it to be sensitive, you may have to go beyond your definition of 'natural', though as far as I'm concerned wrapping some sturdy copper wire around an iron cylinder is far from complex. The iron isn't even necessary, it's the harder part to source.
Self inductance isn't really avoidable, it can also be considered negligible in this application, as it won't 'detect' its own field.