Chiropractic care is very helpful since they can also show you how you are holding yourself and talk about posture-corrective tips and exercises.
The harvesting of Qi exercises at the end of the active exercises can help open up structural blockage as well.
Have a straight back doesn't necessarily mean a stiff, strained experience.in some of the meditations, Master Lin takes you through relaxing from your head to your toes. You can be relaxed and not ramrod straight, while still having that sense of a string holding you up from your crown while your chin is slightly tucked in to straighten out the spine.
Some of what you are talking about can be due to low kidney energy, so get sleep, limit sexual activity, and slowly work up your meditation practice time.
Do a little stretching before your meditation can help to open up that sacrum area, as well as doing the tailbone taps before and when you are done (not to mention at random times during the day when you are walking from here to there). Opening up the sacrum opens up the entire lower part of the body.
stretching, opening up the sacrum (tailbone tapping), and doing what another amazing teacher of mine
taught us about keeping your crown pulled up gently by a thread and dropping/sinking your stress and excess energy from your head down to your shoulders, from your shoulders to your hips, from your hips to the floor, and from the floor to the core of the earth...that's a great way to start your sitting meditations. She's taught this "dropping in" piece to massage therapists, estheticians, nail techs, CEO's, board members all over the world - anyone can benefit from doing that simple presence tool before starting their work or meeting. I'll usually have the people I lead in morning qigong exercises during our retreat do this post active exercises when I have them line up and massage the person standing in from of them. Massage for a bit first, then I walk them through the drop in and then massage the person standing in front of them again. The difference in the presence you bring to it makes a big difference, as it will at your meeting, presentation, etc.
Another little piece for the spine would be interlacing the fingers of each hand (it ends up sort of looking like your spine when you look at it, doesn't it?), and sliding them apart then jamming them together. repeat. Not super hard, but do you feel the impact where they come together at the base of the fingers. Do this for a minute or so to help activate the energy flow in your spine.