As I have my problems with handwriting one straight line from left to right, one solution might be automatic straightening.
One problem here could be that text that is actually set lower or higher is also set to the same height.

Another solution would perhaps be a mode in which temporary help lines appear under the handwriting to show you where you should continue writing.
This would also be good for line breaks.
It would be great if you could also set the line spacing yourself.