The provided context is not sufficient to formulate a detailed answer, so this response is based on general professional knowledge for furniture repair.
Addressing a sunken or sagging leather sofa is a common issue that can often be resolved without needing to replace the entire piece of furniture. The proper method for repair depends on diagnosing the root cause of the problem, which is typically related to either the cushion filling or the support system underneath.
First, you must determine the source of the sagging. If your sofa has removable cushions, the fix may be as simple as refluffing or replacing the inner foam or fiberfill. You can unzip the leather cushion covers and add new polyester fiberfill to plump up the existing filling, or for a more durable solution, replace the entire foam core with a new piece of high-density upholstery foam cut to the correct size.
If the cushions are attached or sewn into the sofa frame, the repair is more involved but still manageable. You will need to turn the sofa upside down and carefully remove the staples holding the bottom dust cover in place. This will give you access to the internal structure. From here, you can often push new stuffing material up into the cushion cavities to restore their loft and firmness.
Should the cushions themselves seem fine, the issue likely lies with the support system. With the dust cover still removed, inspect the webbing or springs. If your sofa uses webbing, check for straps that have stretched out, frayed, or become detached. Broken or overly stretched straps should be replaced. This involves removing the old webbing and using a staple gun and a webbing stretcher tool to attach new, taut straps to the frame. If the sofa has serpentine or zig-zag springs, look for any that are broken or for clips that have come loose from the frame. Replacement springs and clips are available and can be installed to restore proper tension and support.
For a simpler, less invasive solution for minor sagging, you can also place a sofa support board or a custom-cut piece of thin plywood directly under the cushions. This provides a firmer base and can be an effective temporary or long-term fix, particularly for sofas with removable cushions. After completing any internal repairs, simply reattach the dust cover to the bottom of the frame with a staple gun.
