For me, the Intelliskin shirts were too tight.

An alternative is the iPosture device which buzzes you when you slouch. I just started using it a few days ago and so far, so good. On several occasions I have become focused on my computer work and subsequently slouched my back, rolled my shoulders forward, jutted my head forward, then ... BUZZ! I straighten back up and relax into a natural stacked position.

See also, 3rd party reviews:
https://www.google.com/search?q=iposture+review