I always find lower cost couches quickly (3-4 years) get “saggy” wherever people sit the most. I wonder how difficult it would be to source higher quality after

I always find lower cost couches quickly (3-4 years) get “saggy” wherever people sit the most. I wonder how difficult it would be to source higher quality after market springs and replace them. I always feel like it’s a waste to buy a new couch when the old one looks fine but has just lost support.