Biomass combustion in small-scale boilers is a widely used renewable solution for heat production. However, it can lead to significant emissions of gaseous pollutants and particulate matter, especially when low-quality fuels with high inorganic content are used, as it is often the case with potential agro industrial and non-woody residues. To mitigate these issues without increasing system costs, primary measures applied before or during combustion, such as blending fuels with woody biomass and using mineral additives, have shown promising results, as they improve fuel properties, stabilize combustion, and limit pollutant formation. In this context, the objective of this study is to develop technically feasible and cost-effective strategies to enhance the environmental performance of small-scale biomass heating systems while maintaining high combustion efficiency through the use of biomass blends and additives. For the experiments, blend ratios and additive contents were selected based on previous combustion tests with the individual fuels. All blends were tested at the nominal boiler load (55 kW), and the most promising ones were also evaluated at partial load (24 kW) to simulate realistic operating conditions as described in European standards. Almond shell (AS) and exhausted olive cake (EOC) were mixed with pine (50–80 wt.%), while bagasse from grapeseed oil (BGS) extraction was blended with 20 wt.% pine. Results showed that adding pine improved fuel quality and reduced CO, NOx, and particulate emissions, although only the blend containing BGS met all standard emission limits. The AS50P50 (50% AS by wt.) mixture was close to meeting the limits, whereas EOC20P80 (20% EOC by wt.) fulfilled only the CO requirement. The addition of kaolin (2–5 wt.%) significantly reduced gaseous and particulate emissions by retaining alkali species in the ash, increasing combustion efficiency above 92% and achieving emission levels below regulatory thresholds. The combination of pine blending and kaolin proved effective even for very low-quality biomass such as exhausted olive cake, demonstrating a practical strategy to reduce emissions without the need for expensive flue-gas cleaning systems.