Fabric sofas sagging?

[Stringsandthings]

I've found some fabric sofas which are soooo cosy and comfortable however when we sit on them the back cushion seems to sag a bit. Obviously not an issue now but concerned that over time it will lose its bounce and be permanently sagged. Never had fabric sofas before - is this normal?

We’ve had our Vimle Ikea sofa for nearly two years and the cushions are still quite plump/firm. There maybe the one, the back one where I sit the most as i’m home the most which needs to be plumped up more, but other than that they’re all pretty good & to be honest, with two teens, still looks almost new!