@boomerang,
The last time that I was faced with this need,
I went to a furniture store and tried out the chairs
and bawt the most comfortable one; purely empirical.
(Since then, other people who 've sat in it have remarked on how
comfortable it is.)
I recommend this procedure, if that is convenient.
If it is not convenient, then go to the store and be her surrogate.
Get the best one.
David