Any good slalom shaped/length ski will do the trick, Generally the softer FIS skis will behave more predictably, but a good softer beer league ski would be fine (both with a moderate tune 1-3)
With limited mobility, a simple roll on to the edge of the skis will initiate the turn and if balanced will to some part ensure that the skier follows the path of the ski while to some degree forces the correct body position to remain balanced. Please note this is not at race speeds, but at slow to moderate speeds and easy to moderate slopes.
This is why my favorite practice ski for high speed is a high performance SL ski at slow speeds on flatter terrain. You can mimic all GS moves at ultra low speeds developing the feel and timing as a slower pace and no risk. Do it wrong you stop, do it right, its a rush. Step up the pace and initiation step on GS skis and you are pretty close. I've let beginners and intermediates try my skis (BSL size dependent) and watch the joy of the experience of carving turns (sometimes for the first time) with little effort. Ski the SL skis as SL skis are meant to be skied and that is a whole other rush, pushes your skills and reactions to the limit. Remember when pushed they want to return energy for the next turn, when babied they just want to turn when on edge. They don't like straight and flat.
I will add that the correct boot set up will greatly help, in terms of stiffness and forward tilt and so on (this I'll definitely leave to the boot guys as to the best advise here as limited mobility requires a balance of assistance vs hinderance).
I know that this advise goes against regular teaching methods, but it does ensure teach carving and balance in the round about backwards kinda way. There are still other skills that must be mastered, but that's a different discussion.
Carve on, have fun.
