It is tempting to describe the wave function collapse / the measurement procedure as an approximate form of unitary evolution of a composite system consisting of a simple subsystem (being measured) and a much more complex system (the observer). Here "simple" and "much more complex" refer to significantly differing Hilbert space dimensions.

I am looking for the relevant / recent / accessible materials on this subject.

To be more precise: I am interested in toy models, in which the unitary evolution of the composite system looks effectively as a projective measurement of a subsystem.