You can get up to 1cm from stretching your spine with exercises (e.g., with yoga), if you have always treated your spine badly, in my experience. The highest claim I've read on these forums was 2cm, however.
I personally got 1cm, but it (spine stretching exercises) also helped fix my previously terrible posture. Everyone in my family commented I looked taller, despite I have never having told anyone I was doing those exercises. I could never attribute that to 1cm, so it must be from how much my posture improved.
I really want to try glucosamine sulphate, but it's been hard to find locally. I don't want to order it from the internet (only came across shady websites/pharmacies), so I can't share my experience or results with it.