Hi Hypnos,
There is more about the different ways that one mattress can “match” another one in post #9 here.
The mattress shopping tutorial includes a link to a list of the better online memory foam retailers/manufacturers that I’m aware of (in the optional online step) and many of them make memory foam mattresses that are designed to be closely comparable to the Tempurpedic lineup in terms of comfort/support and include which of the Tempurpedic mattresses they approximate in their description.
The single biggest factor in the durability of a memory foam mattress is the density of the memory foam and polyfoam layers (particularly the memory foam layers that are closest to the surface which are generally the “weakest link” of a mattress. There is more about the many variables that can affect the durability and useful life of a mattress in post #4 here but if the foam densities in a mattress are the same or very similar then the durability will be closely equivalent.
It varies by the manufacturer or retailer so the method and any costs involved aren’t the same but generally you would need to wrap the mattress in plastic and put it in a box and if they pay for return shipping then they will arrange to have it picked up and returned or provide instructions on how to return it.
Foundations and frames typically can’t be returned (they can be used under another mattress) … only the mattress.
The better options or possibilities I’m aware of in the Washington, DC area (subject to the “value” guidelines here) are listed in post #2 here but you would need to compare any local memory foam mattresses that aren’t specifically described as approximating a specific Tempurpedic mattress (which are more common with online manufacturers) based on your own personal testing and experience and compare durability based on the density of the foam layers inside them.
There may also be some other mattresses that don’t necessarily “match” the Tempurpedic Rhapsody Luxe that would also be a good choice and there is more about the different ways to choose a mattress (either locally or online) that is the most suitable “match” for your specific needs and preferences and how to identify and minimize the risks of making a choice that doesn’t turn out as well as you hoped for that are involved in each of them in post #2 here.
Phoenix