Typically, I would not recommend that a rider go from a TTR125 to a KTM. Too much height/horsepower difference.
However, since CJ has been stretching her legs on a DR200, it's more of an option for her. I don't know that the KX100 would give you that much "extra" for wheel / ground clearance beyond your TTR, and especially not over the DR that you are riding. The full size wheels give you better clearance over trail garbage such as roots, rocks and logs, plus you can drag along in deeper ruts than you can with a smaller (KX100, TTR) bike.
CJ, do you have any 2-stroke experience? The KDX would be the most similar to the DR you are riding now (if that would make you feel more comfortable). Full height, full suspension, but good tractable, linear motor. And oh-so-easy to start 2-stroke (especially after a fall!) Also, the KDX is probably quite a bit lighter than the DR. The KTM is lighter again than the KDX (by about 10-15 pounds, stock), and has stiffer suspension and another 7HP or so more than the KDX. KTM also has a good powerband, and the addition of a flywheel weight keeps wheelspin down to a minimum. Nether the KDX or The KTM will get you under 200 pounds, though. The KX100 is easily <200, and can be made more trail-friendly with some modifications (flywheel, pipe, etc.) Are enduros in your future? If so, keep in mind the KX100 does not have a lighting coil (you can probably buy one for it, though).
Evaluate what terrain you ride the most, what you want out of your next bike, and go from there. Seat height can be shortened by modifying the suspension, taking out seat foam, etc. Realistically, you'll get it closer to the ground to touch one foot, but don't expect it to be like your TTR.
My recommendation would be KDX, KX/KTM.