I'm playing FA off with K&M and don't find it that difficult. Although I started with it within a week of starting to play the game last September, so didn't have much muscle memory to retrain. It took more to retrain myself to pitch+yaw on mouse instead of pitch+roll another week in.Ah yes. Also one of my good intentions. The flight model that assumes you are generating lift from wings and drag from atmosphere is common in sci fi films and makes the thing easier to fly. To get a true feeling of spaceflight one needs to master FA off. As a keyboard and mouse player... I'm not sure it's possible.
The key to FA off with K&M is to turn on relative mouse. This will make it so after a delay the mouse return to the centre. Play with the rate of return, I prefer a high rate so that you stop acceleration shortly after you stop mouse movement. This is similar to how you can let a joystick spring back to centre, which you can't do mechanically with a mouse.
The yaw on mouse may help with aiming, as you can easier aim with an analogue input than digital, and if you have roll on mouse you have to both roll+pitch to follow minor movements sideways while aiming, which require more thought to execute than just moving sideways.