New covers or a complete cushion?
If the insert still supports you evenly, a new cover may be worth discussing. Foam that stays compressed, has an odor or dries poorly needs a separate assessment; a new cover alone does not fix the insert.
Use old cushions as a reference
Old cushions help explain the original shape, but stretched fabric and compressed foam can distort the measurements. Compare them with the actual frame before approving replacement dimensions.
Refresh a whole set coherently
Count seats, backs, ottomans and pillows separately. Record which pieces share a size and which are different, especially on a sectional with corners or end seats.

