I don't know whether the concern about posture has a medical cause - scoliosis, for example.
But if it's simply a matter of changing habits, then yes. Yes, I do have a suggestion: core strength that's 3 dimensional...
- connection points in the glutes & shoulders
You've already identified two methods for gaining core strength - yoga & pilates. A third option would be to try a "butts & guts" class.
Regardless of what you decide to do, it takes awhile to change habits.