@capt bullshot
It was something like this that I seek. However it seems too "industrial" and the price is very high.
Maybe follow the analog solution with the construction of the conditioning circuit.
I've never seen a typical IC size analog (like the IL300 / HCNR201) isolator. There have been quite a few "analog isolation amplifiers" as a module, way much larger than your space, from several manufacturers (Analog Devices, Knick, ... come to my mind). Quity bulky and expensive anyway.
The Sillabs appnote basically does what the Avago digital isolators do internally (but a bit different, Sillabs implements PWM, Avago uses some kind of delta/sigma modulator.
David Hess' idea to use a Class D audio amp as the modulator sounds quite possible. These are small and inexpensive, and you can use one of these SO08 sized isolators from ADI / TI / Sillabs, and then add a simple low pass filter. Should easily fit into your space if you use all SMD components.