If I understand your existing configuration correctly, it sounds like you have a single pole space on the left and right side of your panelboard at the bottom. The easiest solution is to relocate an existing single-pole breaker to one side on the bottom, thereby freeing up a 2-pole space on the other side.
Using two single-pole 30A breakers (assuming my understanding of your configuration is correct) would function electrically (you wouldn't have two hots on the same phase), but you could potentially damage your equipment if one of the breakers were to trip and the other did not. Plus, it would be a violation of the NEC.
Using two single-pole 30A breakers (assuming my understanding of your configuration is correct) would function electrically (you wouldn't have two hots on the same phase), but you could potentially damage your equipment if one of the breakers were to trip and the other did not. Plus, it would be a violation of the NEC.