I have been on a Tempurpedic Cloud bed (the base model) for 5 months now and I absoutely adore it! For reals. Nothing fake here, I'm a real customer. This cloud had a firmer feel on day one. I could tell it was a brand new mattress. It started to soften up a give each night, and I became very used to it within a week.
I've never experienced a sore lower back from a very firm bed, then again, i've never slept much on an overly firm bed.
I recall the Allura having a very dense feel in that pillow top top layer. That's HD foam, very dense.
I have experienced problems sleeping on a memory foam bed that was too soft from the get go. I had an iComfort Revolution for 4 weeks and my neck was really tweaking from that. It was popping when turning head side to side in the morning.
I can tell you that Tempurpedic quality (and price) easily exceeds that of iComfort. There is not an hint of comparison even between the foundations - the Tempurpedic foundation is a solidly built piece of wood with sturdy, reinforced top.
iComforts come with low-grade 'box spring' foundations doled out with most conventional mattresses.
IComfort also had a problem putting in the actual amount of memory foam they advertised. I clearly caught them in mistaken advertising of having actually an extra 1 inch of memory foam within the mattress, something I didn't want. That helped to explain why the mattress was overly soft.
I stopped in at Sleep Train recently and noticed they brought iComforts in. I'm not worried. I checked out icomforts heavily, Insight, Genius, Prodigy .... they don't compare to TP.