I've answered another question on posture and ergonomics on the Quora platform, where people ask the general public about anything and everything. This is the question I answered:
Do you find posture chairs for the office effective?
No more than a piano stool.
By "posture chair" I assume you mean ergonomic chair. Despite ergonomics being a multi-billion dollar industry, surprisingly, there's no scientific research to support it.
The main issue is that ergonomics tends to try and solve the problem from a mechanical engineering point of view, rather than a behavioral one. It's possible to be just as stiff in a "correct" posture as in a "bad" one. The solution needs to address the psychology of the situation as much as the mechanics.
Chairs are inanimate objects and cannot take responsibility for your behavior. With expensive ergonomic chairs you may fall into one of two camps; you'll either assume the extra money spent is providing more support causing you to take less responsibility for your own behavior, or you'll justify the cost by being more mindful in your behavior. You can do the latter without spending $1,000 on a chair.
In my opinion, the idea of an ergonomic chair for sitting makes about as much sense as an ergonomic floor to stand on, which is why I started by suggesting a piano stool, it's a flat surface that can take the weight of your torso. In fact, sitting and standing are very similar for the spine and torso, you don't sit down as such, but stand up from the base of your pelvis, the sit-bones, or as I prefer to call them, the "stand-bones". The relationship between the spine and pelvis is unchanged between sitting and standing.
The reality is that I wouldn't expect anyone to sit all day in the office anyway, and this is where I make a differentiation between sitting and reclining. Sitting is an activity not dissimilar to standing, where as reclining is being at rest. The main aim of ergonomic chairs is often to help with reclining rather than sitting, but if you can't sit well, you're unlikely to be able to recline well either, the spine being overly curved forward. The "trick" to reclining is to first find yourself sitting well at the back of the chair by standing on your sit-bones , then hinge the whole spine backwards from the hip joints until you come into contact with the chair's back rest. Keep the sit-bones as the main contact with the seat avoiding rolling the pelvis back on to the coccyx (tail bone), which is the common habit.
Seeing as we're all different shapes and sizes, having an adjustable back rest which supports you comfortably is helpful, and where ergonomics can have a useful place, but that's mostly common sense and doesn't require expensive design concepts. Sometimes a cushion is sufficient to find the required support for the lower back.
To be honest, office chairs have improved a lot over the years and a standard chair is usually good enough. I have a cheap office chair I bought from Amazon for less than $100 about 10 years ago and its totally fine.
In the grand scheme of things, if ergonomic chairs were the answer, no one would have back pain from office work and only ergonomic chairs would be available.
If you're wondering how to better improve your behavior/posture/poise so you can use any chair well, I recommend looking into the Alexander Technique.