General advice, please try them before buying as each chair is different and each person require different supports.
A back support will be helpful for some but this only works if your seat depth is deep enough for you and comfortable sit on; otherwise try the “roll’ as described below.
Back support “D roll” or “Lumbar roll” helps to add low back support and since its adjustable it will help to keep your spine aligned; using pillows maybe too bulky for some but this “roll” does a good job.
Foot rest are vital for those needing to raise their chair and get a better arm and elbow support. Make sure you buy foot rest that can adjust the height.
We generally advice people to be examined by an osteopath who can show you the correct sitting posture with the understanding what your job entails. More importantly, even if you have the best chair and best ergonomics, humans are not built to sit the whole day and it is important to keep moving every 45min to avoid muscle fatigue.