I never quite understood the appeal of standing up all day. Having done a couple of jobs in my youth which involved standing up all day and spending 2 hours a day on a train standing up, I couldn't think of anything less appealing.
Over the last couple of years I've been having a couple of problems at work: increasing lower back pain and decreasing attention span. I had no reason to assume either had anything to do with my desk: I, too, rock the Aeron and think it's comfy as heck. I've got my keyboard and monitor at the right height. I take breaks every 30-60 minutes and go walk around. Etc.
But as the back pain kept getting worse, I finally decided to give the standing desk thing a try about 3 weeks ago. I expected my back to start feeling better, and it did -- great! But the unexpected benefit has been vastly increased focus: I somehow feel much more motivated standing than sitting. There's something that feels incredibly silly about watching YouTube or reading Hacker News while standing, and so I just don't do it. I've been more productive these last 3 weeks than I've been in a long, long time.
Perhaps it's just the novelty of a new situation; who knows. But I'm going to stick with it, for now.
Squats, deads, lunges, back hypers, good mornings, and GHRs will do a lot more for your lower back strength than any amount of fiddling with your chair.
Not all at once, of course, but start light and work up.
Muscle is gained when it's subjected to progressive overload. It's lost when no demands are made on it. For most people, sarcopenia (age-related muscle loss) starts becoming pronounced in the 30s. Strength training turns this around.
You'll also find that proper lift posture does a lot for back health -- musculature and spine.
Getting up and walking around through the day helps, of course. But it's not the total solution either.
There have been studies done -- I can't find any on a quick search -- that show that changing a working habit makes them more productive. Then it tails off. Change the habit back, and they get another burst of productivity. So you may be right, and it's just because it's new. Or it may work for you.
I had the same trouble ironically. Blamed my desk and chair for ages. Then I sold my car and it went away. The thing I didn't realise was that the car whilst having the perception of being infinitely more comfortable turned out to cause all sorts of muscle strains.
One of the few things I remember from my ergonomics class several years ago is the professor specifically citing Aeron chairs as terrible ergonomics-wise. His argument was that the less comfortable the chair, the better, as it forces you to constantly shift about to remain comfortable.
I love my Aeron and so does my arse.