Hi LoveWarrior,
If the mattress you receive has the same materials and is the same name and model as the one in the showroom (it would be listed on the law tag) then it would be the same. A new mattress will generally be firmer than a showroom model that has already been broken in though and it will take a little time for any new mattress to break in (generally from about a couple of weeks to in some cases up to about 90 days or so depending on the mattress and the materials inside it).
Different retailers or manufacturers may use different shipping and packaging methods (often several layers of tough plastic wrapping) but the construction date of the mattress will be listed on the law tag as well so you can make sure that it’s relatively new or “fresh”. Your assurance that you are receiving a new mattress is generally the integrity and reputation of the retailer and of course I would make sure that they are an authorized dealer for the manufacturer of the mattress you are buying as well and that the mattress is covered by a manufacturer’s warranty. Comfort or warranty exchanges are used mattresses and aren’t covered by a manufacturers warranty and will generally have a yellow or red tag (instead of a white one that says “all new materials”) to indicate they are either rebuilt or sanitized before being re-sold.
Have you read the tutorial post here and have you made sure that you know the quality/density of all the layers and components in your new mattress to make sure it doesn’t have any low quality materials or “weak links” that can soften or break down prematurely?
Phoenix