For the uninitiated Yoga can seem a bit of a minefield with image after image of the young beautiful holding positions achievable by very few of us, especially if you're starting at our age. I've been practising yoga for around 5+ years now and although I might not always feel I've benefited, I'm sure I have and not just physically. For posture and alignment I think your best style is Iyengar, it's focus is all about alignment. Generally it's not as dynamic and fast-paced as other styles with a heavy focus on ensuring the position is right rather than following a sequence or flow. It relies heavily on props (typically a chair and blocks) and adapts well to people of all levels. An alternative - which I have had little experience of tbh, is Feldenkrais. Check it out. There is lovely lady that lives locally called Sarah Jettoo who teaches both Yoga (not Iyengar) and Feldenkrais who would no doubt be happy to pass on some advice.