Drivers seat foam

I bought a used Octavia and it's great... Aside from the drivers seat making my back hurt. 

The fabric sags a bit when pressed, so I'm wondering is this normal or does the foam need to be replaced?

If so, what's my best option? Just get new foam in or new seat? Could just get a newer seat from a breakers if one from say, a 2018 facelift will fit. 

Driving me mad, car is fantastic bar the back pain the seat is giving me.