In this paper, we report results of simulations, in the framework of both EuPRAXIA cite{Walk2017} and EuPRAXIA@SPARC_LAB cite{Ferr2017} projects, aimed at delivering a high brightness electron bunch for driving a Free Electron Laser (FEL) by employing a plasma post acceleration scheme. The boosting plasma wave is driven by a tens of SI{}{terawatt} class laser and doubles the energy of an externally injected beam up to GeV{1}. The injected bunch is simulated starting from a photoinjector, matched to plasma, boosted and finally matched to an undulator, where its ability to produce FEL radiation is verified to yield $O( um{e11})$ photons per shot at m{2.7}.