Hi Rydray,
I think that post #10 here and the links it leads to may be helpful and hopefully help you avoid most of the lower value choices that you will enounter such as the major brands and most mass market outlets and chain stores that sell them.
As you can see … finding the best manufacturers and retailers in your area is a much more important step than trying to decide on a specific mattress because it will dramatically increase your odds of choosing a mattress that better meets your needs and preferences and also has the quality/durability and value you would want.
Some of the better options or possibilities in the Detroit area I’m aware of are in post #2 here.
This would be no problem with a foam core mattress but if the mattress has an innerspring then it would depend on the innerspring design. Many shouldn’t be bent more than about 20 degrees or so while some (such as those that can be used on an adjustable bed) would be more “bendable” so make sure you check with the retailer to make sure which it is if you go in the direction of innersprings. King box springs or foundations only come in narrower split versions (or the type that can folded up and be shipped through UPS) so this wouldn’t present any problems.
Phoenix