I came across a new interiors site which has posted a few good small apartments, the best (I think) of which are below:-
A 50sqm apartment
I like the flow of this apartment, seen by the floor plan:-
This white apartment is under 50sqm, more like a studio:-
Here is a dark version of an apartment under 50sqm
This apartment is under 40sqm. Every minuscule of space has been utilised.
If you want some Parisian style, here is an apartment under 50sqm.