Hi Gantou,
The first place I would start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines all in one place that can help you make the best possible choices … and know how and why to avoid the worst ones.
I’m not sure where you are in Minnesota but if you are in the Minneapolis / St Paul area then post #2 here has the better options and possibilities I’m aware of that would be close to you.
The tutorial post has more information about how to test a mattress for PPP (Posture and alignment, Pressure relief, and Personal preferences) if you are buying locally and how to choose a mattress if you can’t test a mattress in person and are purchasing online (see mattress firmness/comfort levels in post #2 here). It also has more about the information you will need to make sure that a mattress doesn’t have any weak links in its design and uses good quality and durable materials.
There are certainly many of the members of the forum that think very highly about their SleepEz purchase and are very glad that they had the option to fine tune their mattress after a purchase either by re-arranging or exchanging layers. Of course there will always be exceptions with any mattress purchase but they also have a great return policy for the small minority that have difficulty finding a layering combination that works for them. I also believe that they compete well with the best in the industry and a forum search on SleepEz (you can just click the link) will bring up over 2000 posts with more information and feedback about them as well.
The Morgongava also uses good quality materials but you would need to be certain that it was a good match for you since Ikea doesn’t have as many good options to exchange for another mattress and the only way you could fine tune it after a purchase would be by adding a topper if it’s too firm. There is more about some of the Ikea mattresses in post #3 here and the posts it links to (which include some pictures) and a forum search on Morgongava (you can just click the link) will also bring up more information and feedback about it as well.
Phoenix