Alstom’s INNOVIA 300 straddle monorail vehicle features a single-axle bogie suspended with an hourglass rubber spring. Compared to air springs, the air supply system was removed, but the hourglass rubber spring’s high vertical stiffness did not result in ideal vertical ride comfort. Consequently, we proposed an upgrade and transformation scheme for air spring suspension devices based on existing bogies without upgrading other bogie components. In addition, the steering assist device was optimized, and the adverse effects on the vehicle’s anti-overturning performance were investigated. Based on the simulation results, the critical roll angle of the car body of the air spring suspension is basically the same as with the hourglass rubber spring, and the flexibility coefficient is 10.6% higher, and the impact on the vehicle gauge was examined. Based on simulations and tests, there is a significant improvement in vertical ride comfort. The scheme can be applied to engineering applications.