Sofa seat cushion inners

I have a 6 year old IKEA Karlstad sofa in my livingroom, now discontinued. It's still in really good condition as I have the original light grey covers it came with (I use these in summer) and I had another set made up by Bemz in a teal coloured heavy coloured cotton (for winter).

The back cushions are fine, the seat cushions are still comfy but I'd like to replace them at some point to make them firm again (I rotate everything so it gets even wear). Does anyone know where I could get firm seat inners, I've tried searching on the internet for companies in Switzerland but so far have come up with nothing. It would be a shame to replace the sofa as it still has a lot of life left in it and we like the simple modern shape.

It'll be cheaper from Germany

https://www.schaumstofflager.de/scha...29c8b9b8f7fa4d

Searching for Schaumstoff Sitzkissen Zuschnitt brings up lots of results.

You'll want to spend some time figuring out exactly what kind of foam cushion suits your needs. If in doubt, I'd email the supplier and ask their advice