While picking an office chair to work from home, what are the features to look for? Are the two features - additional lumbar support and a headrest really important? Why additional - most office chairs come with a structure that supports lower back and then curves away into a recline position.

Generally the office chairs have a mesh back which wouldn't provide enough lumbar support on its own. Hence, the need for additional support.

A doctor recommended mid-back and not having headrest. Tall chairs restrict shoulder and neck movements especially when sitting for long time - he recommended periodic shoulder and neck movements (rotations) to avoid pain. Chair height a little below your shoulders (aka mid-back) is good enough. Lumbar support is extremely helpful.