Why don't you just get a simple loose ring/D-ring/Eggbutt snaffle or french link snaffle? If she's truly light in the mouth, you probably won't need anything more than that. And if she isn't as light as you were told, a snaffle is the best choice to retrain her to be light.
And, if she neck reins, you can still neck rein in a snaffle. People may tell you that you can't neck rein in a snaffle, but you totally can.
In any case, I'd start with a simple snaffle (no shanks, etc) and then if she shows that she can neckrein like a pro and you never need to actually have contact with her mouth to get her to respond, you could move up to some kind of short shanked curb, but only if you want to. If you're just trail riding, you might just end up the happiest with a snaffle.
But anyway, a snaffle is good stuff.
Personally, on my mare, I love my bitless "Indian Bosal" that I bought off ebay. I can neck rein in it a little easier than the snaffle (not sure why, my horse just likes neck reining in it a little better. Horses! lol) but I can direct rein just as easily. However, not all horses like being bitless, but that is an option, if you feel so inclined.
Also, with the "Indian Bosal" some people think it doesn't give enough release. I've found that releases enough with my mare that she doesn't get confused by it, but it is tight-ish (just basically as tight as a properly fitted bit would be against the corners of the mouth) at all times, so that would be something to watch for if you're concerned by that.
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.