hi all - what a mixed up confusing shopping experience! took me 8 mo of fighting sleepy's to get a warranty honored for my kingspring horrible bed! I am in a quandary for reliable info. looking at a dormia bed and cannot find enough info. anyone have any type of experience? I like firm mattresses that DO NOT CAVE!

Innersprings with interlaced coils (coils are wired together ) are probably the least likely to sag.  I know that is the way Sealy makes them.  Their top of the line with the most coils (782 in queen?) seem firmer than the ones with less coils.  What you want to avoid is a lot of layers of foam on top (i.e. plush, pillowtop, ultra plush, etc.).  Those layers will evenentually sag. 

You could also go with a base of extra firm latex (especially dunlop process), and have a few inches of medium latex on top for comfort.  Latex should last pretty long without sagging.

Dormia makes an interesting product, although I think you may also want to consider the Sensation by Natura if you can find a dealer in your area....similar beds really (memory foam on top of latex base).  the difference is the natura will also have a layer of wool on top for a little bit better temperature regulation.  pricing should also be similar.  i don't think either one (dormia or natura) is likely to cave in a hurry.  or consider going to an all latex build in a firmer feel, that would be likely even more durable....question is if you find them comfortable or not.

I might take Sandman's advice and go with the Sealy with springs he mentioned. I haven't tried them but this does sound good.

I'll go even further in saying buy the absolute firmest model Sealy makes (or whatever brand you buy). Not just the firmest in the store, but ask them if they offer a super firm "rock like" model, then order that.

Plan to put some soft latex on top as a topper but don't let them talk you into getting a softer model with the built in topper or pillow top, because that will be made of cheap foam that will break down very quickly and hurt your back.

Also, if you get the model as firm as you can, if it does not feel good, do mattress surgery on it and take out what little cheap foam they put in it and add your own latex instead.