Hi Hu,
There’s much more information about an appropriate foundation in the foundation thread here.
You seem to be describing some sort of a semi-flex or min-flex wire grid network foundation. You’d want to inspect your current foundation to make sure that it is not sagging, as these wire grids can bend inward over time, and also to make sure that your foundation is not sagging when weight is placed upon it, either from a wire grid network that is allowing for such sagging, or from an improper frame without center reinforcement underneath the foundation.
Ultimately, you’d want to defer to the advice of any mattress manufacturer you’re considering, as they will advise you as to the appropriate type of foundation that their mattresses need to be placed upon for both optimal performance and warranty maintenance. Some stores recommending a new foundation can do so as a manner to get you to spend a little extra money, but in other cases it may be a necessity because of the type of mattress you’re purchasing, or the inappropriateness of your current foundation.
Phoenix