Light meson physics and scale setting from a mixed action with Wilson twisted mass valence quarks

We consider a mixed action approach where valence Wilson twisted mass (Wtm) fermions at maximal twist are combined with CLS ensembles consisting of $N_f$=2+1 flavours of O($a$)-improved Wilson sea quarks. We present an update of the results of the matching of valence and sea quarks, and of the subsequent continuum-limit scaling studies of light-quark observables. A scale setting procedure combining the results from the O($a$)-improved Wilson setup to the ones from the valence Wtm regularisation is discussed.