Hi DJD,
I’m not sure how you are defining a “European mattress” because there isn’t really a specific definition of a European mattress and there are many types of mattresses that are sold in Europe (just like in North America) but the better options or possibilities I’m aware of in the Milwaukee area (subject to the guidelines here) are listed in post #2 here and for the Chicago area are listed in posts #2 and #4 here.
The foundation post here also includes more information about the different types of support systems that are generally suitable for different types of mattresses and some good sources for each of them (although most good retailers/manufacturers will also have a foundation that is suitable for the mattresses they make or sell).
Phoenix