as far as any bending, you should be bending in your ankles, knees, and waist. Your upper body should remain pretty static. If you spend a lot of time in the bumps you might want to get shorter poles, and limit your pole touch movements to you wrists (your pole touches are when you are in a compacted state and are not too far in front of you - you shouldn't be reaching way out). Ideally your tips should always be driving into the snow and reaching for the next bump.
It shounds like you have a good idea as to what you need to do and what is right (correct stance, balance point and whatnot) just sounds like you could use some practice and ideas. One thing you can do to practice (out of the bumps) is called pivot slips. Its a straight side slip, where your skis have to be flat and basically as you slide sideways your skis do 180 degree turns under you (just think about turning without turning - your momentum continues down the fall line, your skis go from side to side, and your upper body remains pretty constant and facing down the hill).
I would be willing to bet that if you started steering your skis a little more your upper body and pole touches would probably smooth out a little (and remember to keep your feet under your body - not as easy as it sounds).
Biggest trick to steeper lines and deeper troughs is speed control, which is harder to do if you are zip-lining. You need to use the amount you absorb, the amount you steer the skis, and the amount pressure you use when you hit the bump and go into the next one. Try going a little slower than normal in the steeper lines (which will force you to have proper form).
Also, why not attack the bumps with multiple tactics. I ski bumps probably about 3-5 different ways each bump run. Keep practiceing your zip-line, but develop a more fluid method too. The more different techniques you are comfortable using the better you will be able to adjust to the terrrain and conditions. 1 approach is not always the right answer (although it might be a little more fun).
When you practice go as slow as possible, speed hides all flaws, going slow will allow you to tell what your skis/body/movements/terrain are telling you. Once you learn to ''listen'' to all the variables, and you are comfortable with the movements/skills you need to attack the bumps, you will be more confident, less likely to panic (not saying you do now), and smoother through the line of your choice.
One last thing, don't forget to pay a lot of attention to what is coming up, if the line sucks, get out or change it, be ready/expect the unexpected, and you'll be skiing better in no time. Just remember that things don't change over night, they take time.
I hope I didn't forget anything, my fingers hurt.
