Relative humidity (RH) is one of the most important parameters, not only influencing indoor comfort and air quality, but also impacting energy performance and durability of the envelope. To minimize health risks and discomfort, the optimal range for indoor RH lies between 30% and 60%. This experimental research reports the development of cement mortars with enhanced potential to passively adjust indoor RH levels, achievable by introducing superabsorbent polymer (SAP) and porogene additives—vermiculite (VER), and perlite (PER). Samples with 0–2 wt% SAP, 0–5 wt% VER, 0–5 wt% PER and 21.5–43 water/solid weight ratio were produced to estimate the individual performance and optimal dosage of mentioned additives. In general, the additives showed distinct behaviors, but samples VER and PER containing 2 wt% exerted less influence on the mechanical properties, while the moisture buffering value (MBV) results remained at same level of the ones of the standard and non-additivated formulation (reference mortar—REF). However, the 2SAP sample with 2 wt% superabsorbent polymer predominates on most of properties, reaching the maximum MBV results, but a higher unrestrained shrinkage values and strong reduction of mechanical properties was also obtained. For that reason, the optimal SAP dosage is limited up to 1 wt%, since it exerted small influence on the standard/common properties required for the mortar given it the classification of good, according to MBV determinations conducted by following the Nordtest protocol.