But in this case "better" is the difference between some isolation and complete isolation without any noticeable movement at all. The difference between a pocket coil and memory foam in terms of motion isolation is night and day. Like comparing a waterbed to a slab of concrete.

Remember that even with pocket coils, the pillow top, as is most common today, is still shared across the entire bed and contributes to the motion. Yes, they're dramatically better than an older non-pocket mattress, but the difference when comparing to memory foam is infinitely greater.

And a box spring will definitely cause more motion as well. We have our current mattress on two double-sized adjustable slat bases. Tons of configuration possibilities. I'm actually going to swap out one of the layers on my side for additional firmness soon.

As far as returns go, I'm pretty sure it's not legal to sell a used mattress even in the US. You can't do it here in Canada. You can't even bring a used mattress across the border from the US. Pretty sure that when I bought from places with such claims that they said the mattresses are either destroyed or donated.