Hi TheholyLancer,
The first place I would start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you make the best possible choice no matter which type of mattress you tend to prefer … and perhaps more importantly know how and why to avoid the worst ones including the major brands or any mattress where you can’t find out the type and quality/durability of the materials inside it (see this article).
There is more about the different ways that one mattress can approximate or “match” another one in post #9 here but I certainly wouldn’t consider any mattress that used comparable quality materials to most of the Sealy mattresses because the major brands tend to use lower quality materials in their comfort layers than I would be comfortable with considering and I would look for a mattress that uses higher quality materials that is better value than any of the major brands.
Quality and durability aside though … “feel” is the most subjective part of comparing mattresses and a mattress that “feels” the same for one person may feel very different to someone else. I also don’t know of any other manufacturer that makes a mattress that is specifically designed to feel the same as the mattress you are considering so the only way to know whether another mattress feels the same to you (regardless of whether it would feel the same for someone else) would be based on your own personal testing either in “real time” or with very little elapsed time in between testing both of them (our memory of subjective comparisons such as “feel” don’t last very long).
I would avoid using another mattress as a “target” (which may not even be the best match for you in the first place) and rate every mattress you consider against a common set of criteria based on the parts of your personal value equation that are most important to you.
I would also pay much more attention to the quality of the materials in a mattress than the length of a warranty. Warranties have little to do with the useful life of a mattress because they only cover manufacturing defects and not the gradual (or more rapid) loss of comfort and support which is the main reason that people need to replace their mattress. Longer warranties are often more about marketing than they are about the durability or useful life of a mattress. There is more about mattress warranties in post #174 here.
I’m assuming that you live in Canada and are visiting the US for a while? I’m not clear why you are concerned about not being able to use a mattress that you purchase in another country but if you purchase a US made mattress in the US and then either ship it or bring it across the border into Canada you would need to pay taxes (or brokerage if you are shipping it) but there is no duty (see post #2 here). It would also qualify for any exemptions that you are entitled to if you bring it back with you based on the length of your stay.
The better options or possibilities I’m aware of in the areas around San Francisco area (subject to the guidelines here) are listed in post #2 here.
If you let me know your city or postal code in Canada I’d also be happy to let you know about any of the better options I’m aware of that are reasonably close to you if you wish to purchase your mattress in Canada instead.
There is also a list of the better online retailers and manufacturers I’m aware of that ship across Canada in post #21 here that may also be helpful if you are open to considering an online purchase.
Phoenix