Some people have been using the FMA copilot on their Corona heli. This is a device which will "level" the helicopter for you if you release (center) the cyclic control. It will not work indoors because it needs to see the horizon to work properly. It does not replace a gyro, so you will still need a gyro.
The FMA copilot is nice, but really isn't really necessary unless you are having problems learning hovering. If you have a limited budget, then it is more important to buy a good heading hold gyro than the FMA copilot.
Also, you will likely outgrow the FMA copilot after a few months and remove it whereas you will not outgrow a good heading hold gyro. Therefore I recommend buying a good heading hold gyro first, and purchasing an FMA copilot later if you become frustrated with learning hovering.