Some years ago, I did Pilates once a week. It was great for tone and flexibility. I don’t know if it specifically helps with posture, but you know that wobbliness that you can get trying to do a slow controlled movement? Its good for that kind of stuff. It does take time and consistency though, not a quick fix. A lot of posture problems can come from lack of core strength, both Pilates and yoga would be good if that’s where the issue is.