Hi Hilliap,
The first place i would start is post #1 here and the information, steps, and guidelines is links to. This will help keep you away from the major brands and the local chain stores which (as you have seen) will waste a lot of your time and lead to more confusion than anything else. The less time you spend in these types of places … unless you know exactly what you are testing …the better.
Some of the better options and possibilities I’m aware of in the Detroit area are listed in post #2 here.
I personally wouldn’t spend any time at all at any of the local big box places even for testing unless you knew specifically what you were testing there and why. No matter how you feel on these mattresses … for the most part you won’t be able to find out any meaningful information about their quality or value or what is in them. There are certainly enough other choices around you that would either be good local value or could provide a guideline for an online purchase if that becomes necessary or desirable.
Just to be clear … most only allow this once … not an unlimited amount of times. Some allow either the return or exchange of the entire mattress with various costs connected to this and some offer layer exchanges where you can fine tune the mattress you already have … again with various different costs connected to the service (usually low). This certainly lowers the risk of an online purchase but it isn’t risk free either.
First of all I would focus on local outlets and then add online if that became necessary (I wouldn’t start of with the assumption that online is the direction you are going). If you are going by specs … it would be important to try to make “apples to apples” comparisons and you may not have access to mattresses that use the exact same materials and layers. It would be more realistic to expect that you would be “approximating” another mattress (if the materials and layers were the same) rather than “duplicating” it and to build in the expectation of either re-arranging the layers if that was an option (usually this is an option in higher budget ranges than yours) or a layer exchange if necessary. ILD is only one of many parts involved in approximating another mattress (type of materials, layer thickness, cover material, quilting, and others). The best approach is to test local mattresses as much as possible and then to add online options if that becomes necessary and any difference in value justifies the extra risk. Either way … local testing on different types of mattresses is an important part of the process.
The more testing you do on mattresses with known materials, ask questions, and talk to people … the closer you will get to knowing your ideal choice.
Phoenix