The new one looks proportionally closer to that reference and reads more like an adult proportionally I think. Assuming it's not a bendy-straw style you're going for I'm not that fond of the U leg or the back though, so I went out to help those a bit. Am not a master and all that, but-
I drew a bit of a skeleton on your thing guessing how it'd go, but it's probably not proportionally correct because I didn't want to overwrite yours.
(and also because I am not actually very experienced in anatomy)
Although I can't find how the parts of the spine contribute to flexing forwards, it's definitely not one part making a 90 degree bend. ^^;
-Based on trying to pose myself for a minute or so, the supporting arm (here left) would be straight resting on the hand instead of the lower arm if the shoulders are at the height of the knee.
-If they're leaning that far back the supporting arm would have to angle further back rather than next to their side. This has the added benefit of separating it from the torso!
-I mostly removed the sharp corner from the torso bend and it looks a bunch more natural. I think.
-The leg comes into something of a point at the knee (at this resolution anyway), and the 3/4? angle means the thigh obscures the calf partially.
-Bent the elbow a bit just so the arm isn't a straight line, but that can be a matter of taste.
I should probably have kept the left leg as long as you had it, but that's because I only did the posing after editing.
Hope this helps a bit.
