Dense blockwork has a conductivity in the range 1.1 to 1.2 W/(mK).
13mm Dense gypsum (1300 kg/m3) has a conductivity of 0.57 W/(mk).
13mm Densure gypsum (1000 kg/m3) has a conductivity of 0.4 W/(mk).
Render, cement/sand, has a conductivity of about 1.0W/(mK).
Render, gypsum/sand, has a conductivity of about 0.8W/(mK).
Consider render with thin, 3mm, gypsum finish?? (a bit experimental as may crack due to differential propoerties.)
Though if you think about the wall as a whole the insulation is likely have a conductivity of < 0.04 W/(mK). Does it matter? Even with gypsum the lamda is >10x greater than that of insulation.