My elderly in-laws have a couch that allows you to sink deeply into it
when you sit. Because of their physical infirmities, standing is
difficult. The frame of the couch is in tact. None of the frame is
broken or drooping. The cushions look fine, but I'm sure they have lost
some of their support. My theory is that the springs supporting the seat
cushions are worn.

Assuming that my theory is correct, does it make sense to try to get the
springs replaced? Is there a snowball's chance that a furniture repair
person or an upholsterer would be able to replace the springs? The sofa
is not a sleeper version. It's just a sofa.

The couch is in great condition otherwise, and the in-laws are not
amenable to buying new furniture. Any thoughts?