Yes, co2 increases quality as well... denser buds.
With a controller like the chhc-1 or igs-220 you'll be able to control your temp, humidity and co2 at the same time. It's a big initial outlay in cash, but you'll get it back in one cycle, I promise.
For now, you can put a speed control on your can fan as well. It's not ideal, but a $5 dimmer switch at home depot works as long as you don't try to run the fan at too low of a speed... or run the fan on a thermostat, you can get a line-voltage t-stat at Grainger for about $25.