Hi LM,
There are no exact sizing standards in the industry for mattresses or components and they can vary slightly from manufacturer to manufacturer depending on the dimensions of the materials in the mattress that they order and the thickness of the cover that goes around the foam layers or components (the foam layers are always smaller than the final dimensions of the mattress itself).
You can see Serta’s standard sizing and variance here and if a mattress you purchase is outside of their standard dimensions then it would be “out of spec” and would be a warranty issue.
Only you can feel what you feel on a mattress or decide on the types of mattresses and materials that you are most interested in trying or that you tend to prefer and there are too many unknowns, variables, and personal preferences involved for anyone to know which specific mattress design or combination of materials would be best for you based on specs (either yours or a mattress) or “theory at a distance” (see mattress firmness/comfort levels in post #2 here). What is “best” for you either in terms of a mattress or a manufacturer/retailer can be very different from what would be “best” for someone else.
There is more about the most important parts of the"value" of a mattress purchase in post #13 here that can help you make more meaningful comparisons between mattresses but it will come down to …
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Testing for PPP (Posture and alignment, Pressure relief, and Personal preferences) hopefully using the testing guidelines in the mattress shopping tutorial.
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Checking for the quality and durability of the materials inside the mattress to make sure there are no lower quality materials or weak links in the mattress (see this article)
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Comparing for value based on #1 and #2 along with all the other parts of your personal value equation that are important to you (including the two preferences you mentioned … temperature regulation and edge support)
There is more about the many variables that can affect sleeping temperature in post #2 here. A mattress that sleeps warm for some people may be fine for others depending on where they are in the oven to iceberg range and on the temperature and humidity in your bedroom but the mattress protector or any mattress pad you are using, your sheets and bedding, and your bedclothes can all have a significant effect on sleeping temperature regardless of your mattress and in some cases changing these may be all that is necessary to keep sleeping temperatures inside the range that you are comfortable with. Gel memory foams can be cool to the touch but they tend to have a temporary effect on sleeping temperature when you go to sleep at night but it doesn’t normally last throughout the course of the night (see post #2 here).
You can see some comments about the Vantage in post #2 here and as you can see I would avoid it along with most major brand mattresses or any mattress that uses too much in the way of lower quality materials that would be an obvious weak link in the mattress or where you aren’t able to find out the quality and durability of the materials inside the mattress (see the guidelines here).
With the Sherwood mattresses your chances will be higher that you can find out the quality/density of the materials inside the mattress so you can make a more informed choice about the quality and durability of a mattress you are considering.
Hopefully you will be able to get a refund and start all over again so that you will have much better options to choose from. If this happens then the first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that you will need to make the best possible choice … and more importantly know how and why to avoid the worst ones.
If you are only able exchange your mattress for another mattress that they carry then you would be in a more difficult position with more limited choices. If this turns out to be the case then post #2 here has more information about the two different strategies that you can use to help you make the best out of a more difficult situation. Which one of the two strategies would be best for you will depend on whether any of the mattresses in the store are a good “match” for you in terms of PPP and on whether you can find out the specifics about the quality and durability of the materials inside any of the ones that are to make sure they don’t use lower quality materials or have any obvious weak links in their design.
Phoenix