3x per week. Start with an empty bar, then add 5lbs to the bar each time you deadlift. Once it gets so heavy that you can't add anymore, just back off to 1-2x per week and maintain the weight on the bar. It'll take you about 20 minutes each time and the bar and plates will take up about 4 square feet in your living room or garage when not in use.
Here's how you deadlift: https://www.youtube.com/watch?v=VGZrATR1O4E
You can get a barbell and plates on Craigslist for $250. If you decide that it ain't for you, you can sell your barbell and plates on Craigslist for $250. So there is no financial downside. But it has the potential to be the best $250 you have ever spent. On anything.
Week 1 - 10 min stand, 50 min sit.
Week 2 - 20 min stand, 40 min sit.
Week 3 - etc...
Postural muscles take time to develop. Do the Agile 8 every day to work on your flexibility. https://www.t-nation.com/training/defranco-agile-8
The shortcut to an iron back is deadlifts, find a quality trainer and get in the gym for 30-45min 3x a week and you'll really improve.
As an alternative to the deadlift, I'd like to suggest the two-arm kettlebell swing. While there's no magic bullet in training, the kettlebell swing seems to come pretty close [1]. Plus, you can get one for home/work if you don't want to go to the gym.
I would however second the recommendation of learning exercise technique from a qualified trainer, particularly for hip hinge exercises - most adults, myself included, seem to suck surprisingly hard at what is one of the most fundamental human movements.
In case you do decide to go the YouTube route however, at least learn from a quality resource like StrongFirst [2], there's too many technique videos ranging from ineffective to plain dangerous.
[1] http://www.strongfirst.com/optimizing-back-health-with-the-k...
Esther did a talk at Google in Mountain View in 2008 > http://gokhalemethod.com/video/authorsgoogle maybe she could do one at Google in Seattle during her trip? Get in touch! info@gokhalemethod.com
Cheers
For many people back pain is actually caused by weak abdominals. The imbalance puts things out of whack. I also DL heavy (2-3x BW at my best), and if I also was not crushing my abs I would get back pain.
The body can be a mysterious machine.
I've got a standing desk as well. But standing is no substitute for exercise, which is what your back really needs - both the movement and the strengthening.