Take the €600 and run. They don't have to give you a full refund. They're within their rights to firstly repair the beds, which they did, and secondly replace the beds, which could come next if you keep complaining. And that'd be more hassle than it's worth, having beds removed and new beds of same quality coming back in.
You possibly could get them for fit for purpose, but then again, they're nearly a year old now, and you've used them for sleeping on since then, so they're obviously doing their job as beds.