If you pop into the Geant hypermarket in Beziers, they have exactly what you
are looking for on one of the temporary displays in the main entrance area -
a commercial product designed to cover old stairs, available in a variety of
finishes. Unfortunately, I didn't take a note of the company, as it was not
of interest to me at the time.

If it's that cladding system you see around markets in France, run away.