Though my default flying is joystick and rudder peddals with realistic mapping
I bind mouse left/right to Turn left/right. Turn uses a mix of rudder and roll depending on speed so when very slow or hovering its becomes fine rudder control. That leaves A&D for left/right cyclic when you need to move sideways from hover.
other bindings, W&S for collective.
PS. I get your objection to 'Turn' but for noobs on keyboard and mouse this is probably the easiest way to fly. And doing less with the left also makes it easier to reach the alt for free look. If the lack of 'sim' bothers me I just reach for my joystick.
Also to be honest I'm not sure what to make of the description above. The default A3 keys are as you request, its just a question of exactly wich keys you want bound to task. You havn't actualy suggested your alternative.