You've got lot's of advice so far so I'll try and keep it short.
You mention it moves around a lot at 6-8ft or so off the ground? Couple of questions regarding that: Are you at a high angle of attack at this point? and when you land do you feel like you've 'dropped' it on rather than flown it on?
If that is the case I'd suggest you are rounding out to much in that first phase and not getting into the nice ground effect area - so you end up pulling back and 'waffling', or stooging - often accompanied by the stall horn and dropping onto the runway.
I only mention this because when coming from a larger plane, with much more inertia and weight, that round out height (or phase one) would be fantastic as you have the right combination to settle it on, but being light and nibble you have to get a bit lower in phase one, and then start the landing phase two. (i.e. the hold off)
I'll probably get boo'd at, but maybe try a flat power on approach a couple times (keep that nose wheel off however!) but that way you might be able to find the ground and the sweet spot to level off at.
Ps. I'm not an instructor, but I've had a mix of aircraft type experience and this is something that I notice people do, and I've done myself.
regards