When we bought Amy's new bed, we also bought new slat bases (? -- Lattenrost; the frames you put underneath the mattress, with [often springy] slats to bear your weight) and new mattresses for ourselves. Our frames were slightly broken, and our mattresses were about eight years old, and apparently you're supposed to buy new ones every ten years or so.
(Stella and I sleep in a double bed, but we have separate lower frames, separate mattresses, and separate bedclothes. Some people get along just fine sharing a double-width mattress and sharing a duvet, but I'm not one of them. We also have mattresses that are slightly wider than usual -- 100x200 cm [3'3"x6'6"] instead of the more common 90x100 cm [2'11"x6'6"] --, which helps.)
Stella bought a hard mattress; I wasn't sure what kind was best for me, but given that I sleep on my side/shoulder a fair bit, I thought something a bit softer would be better. The salesman (who seemed very helpful and nice) said that as long as I didn't take the mattress out of its plastic covering, I was welcome to sleep on it at home for a week or so, and I could still return it if I ended up not liking it and needing something harder or softer. So I picked one that was a bit softer than Stella's, but still rather firm.
So, we got home, and I put my mattress on the bed, complete with plastic covering. Stella ripped her covering off, lay down on the mattress, and sighed contentedly. "Ah, this is much better."
However, come next morning, things were different: she said it had been like sleeping on a rock. I wasn't completely happy with mine, either; my shoulder felt a bit unhappy, so mine was probably a bit hard to me.
Now we had a problem. I could easily return or exchange mine, but what about Stella? She was pretty disappointed and frustrated at the prospect of a fair chunk of money down the drain. Since she had already taken off the plastic covering, she probably couldn't return hers. (Though she did put on a special mite-proof covering, plus a fitted sheet, before sleeping on it.) She considered getting rid of them on eBay, but I'm not sure how well such large, bulky items sell.
Anyway, we ended up going down to the shop and explaining our plight. Fortunately, the salesman we had talked to the first time was there, and we told him what had happened. He said there wasn't a problem -- as long as we had the original plastic covering, she should put the mattress back and tape up the slits where she had cut it open, so that it wouldn't get dirty or damaged during the return journey, and they'd pick the mattresses up. A stone fell from Stella's heart, as they say in German.
He also offered to sell us some new mattresses. We had considered simply going back to our old ones (Stella said that with the new frames, she felt that she was already sleeping a bit more firmly than with the old ones), but we ended up buying new ones. Not least because he gave them to us at 25% off "because we are such good customers". (Stella wondered whether the salesman was the branch manager, that he was authorised to give us such a fairly large discount.) So we'll be trading in the mattresses we bought and buying new, softer ones (more expensive, too). The salesman said we shouldn't worry too much if they seem not quite right, either, since it takes a body a while to get used to a new mattress; we should feel free to test-sleep in them for a week or even two before we throw in the towel. (Is that an English idiom, too?) (Though Stella said she didn't think she could have slept with the wrapper on, because it rustles whenever you move, and Stella tosses and turns quite a bit more than I do.)
Those'll arrive on Saturday, probably, so we shall have to see how things go there.
I've still got the new mattress on, but might switch our old one back in tomorrow. (Stella already did so today.) Then we'll sleep on those until the new ones arrive.