Hancock & Moore Cushions

[henboy]

I read with interest your comments about sagging seating. Photos attached.
We have a Hancock and Moore 2038NB Austin with a sagging problem. The chair is has become very uncomfortable, and I am somewhat surprised as the chair has had limited use in the 10 years we have owned it.
The webbing seems taunt to my untrained hand, but I did notice that there is no webbing on the back quarter of the seat. Is this normal?
I an guessing the solution is to tear the chair apart and re-do the webbing, which would seem expensive. We have considered adding a piece of foam under the back 1/3 of the seat as an alternate solution.
I would appreciate your comments and advice.
Thank you.