Asking again, due to lack of any recommendations before.
It is needed for a one-bed flat (for central heating and DHW) - about
60 sq mtrs floor area (kitchen + bathroom with bath + living room +
bedroom). One rad with TRV in each room. Biggest room is 4.5 mtrs x
4.5 mtrs. Flu will go straight out through the cavity wall on which
the combi will be fixed.

Thank you,

Duke