Hi mkbm,
Just in case you haven’t read it yet … the first place I would start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you make the best possible choices … and know how and why to avoid the worst ones.
Other than careful and objective testing that can tell you whether a mattress is a good “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) … a mattress is only as good as the quality of the materials inside it regardless of the name of the manufacturer on the mattress or the length of the warranty. A warranty only covers defects in the material and has little to do with the useful life of the mattress or how long it will keep its comfort or support (see post #174 here about mattress warranties).
Besides making sure a mattress is a suitable choice for your body type, sleeping positions, and personal preferences … it’s always important to make sure you know the specifics of all the layers inside any mattress you are considering so you can identify any weak links and make meaningful comparisons with your other “finalists”. There is more about the information you need in this article and the foam density guidelines I would suggest using are in post #4 here.
If you can list the specifics of the mattress on the forum (including quality/density of all the foam layers) I’d be happy to make some comments about the quality of the materials and help you assess whether there are any weak links in the mattress.
You can see my thoughts and comments about Sean and My Sleep Nation in post #2 here and in post #2 here which also includes some of the other options and possibilities in the Denver area. A forum search on sleepnation (you can just click the link) will bring up more information and feedback about them as well.
Phoenix