I'm not sure I can give a persuasive answer, if you find melees troubling. I haven't found it a problem that charges do not always have decisive outcomes. For me, melees seem to resulve in a few turns, often when a new unit can join in, and that is Ok for me, rather than frustrating. Maybe it depends on the troops you are using. If I think of a clash between pikes and legionaries, I expect it to be somewhat of a grind. I imagine troops backing off from combat several times before one or other begins to give way (becomes disordered). Then it becomes a question of whether the disordered unit can rally (low probability) before giving way completely (breaking). I don't find the results 'wild'; good troops tend to come out on top.
I can se that you could make things more decisive by changing the probabilities of disorder in the way you suggest. It would increase the benefit of being the charging unit. Some units could become significantly more powerful - it would become much more likely that a unit attacking the flank or with the 'lance' option would break its target. Maybe that is what you are looking for. Personally, I prefer the possibility that a charging unit may get a poor card and find itself worse off than the unit it charged. I suppose it depends how much chance you want in your games. I don't think having a reasonably high chance level must make the game 'beer and pretzel'.
As to the cards, you could use D10 or the chits Simon sells. I like the idea that, once I turn a card, I know only too well what I should have done, which maybe not what I've chosen to do. Dice and the chits don't give that. Again, that particular experience may not be something that you want.