The paper presents a novel method for designing quasi-isodynamic (QI) stellarators, which are candidates for fusion reactors. QI stellarators are a type of magnetic confinement device that uses twisted magnetic fields to confine a plasma, similar to tokamaks but with different advantages. The authors introduce a new optimization method, called Stable Quasi-Isodynamic Designs (SQuIDs), which aims to minimize turbulence and improve plasma stability while maintaining excellent fast ion confinement and low bootstrap current. The SQuID design is compared to an elongated QI configuration and the Wendelstein 7-X (W7-X) stellarator, a world-leading experimental facility. The SQuID configuration shows better performance in terms of turbulence reduction, fast ion confinement, and MHD stability, making it a promising candidate for a next-generation fusion reactor. The study also highlights the importance of the max-$\mathcal{J}$ property, which improves fast ion confinement and reduces turbulence. The results suggest significant flexibility in the design of reactor-relevant QI stellarators, opening up a wide range of potential configurations.The paper presents a novel method for designing quasi-isodynamic (QI) stellarators, which are candidates for fusion reactors. QI stellarators are a type of magnetic confinement device that uses twisted magnetic fields to confine a plasma, similar to tokamaks but with different advantages. The authors introduce a new optimization method, called Stable Quasi-Isodynamic Designs (SQuIDs), which aims to minimize turbulence and improve plasma stability while maintaining excellent fast ion confinement and low bootstrap current. The SQuID design is compared to an elongated QI configuration and the Wendelstein 7-X (W7-X) stellarator, a world-leading experimental facility. The SQuID configuration shows better performance in terms of turbulence reduction, fast ion confinement, and MHD stability, making it a promising candidate for a next-generation fusion reactor. The study also highlights the importance of the max-$\mathcal{J}$ property, which improves fast ion confinement and reduces turbulence. The results suggest significant flexibility in the design of reactor-relevant QI stellarators, opening up a wide range of potential configurations.