While neither the iComfort or the Novaform gel memory foam are an “adjustable mattress” both can be used on an adjustable base as can other foam core mattresses (including latex mattresses) or an innerspring mattress that is made to bend without damaging the mattress. The adjustable base that makes these sleeping systems adjustable is purchased separately.
There is a “self contained” mattress which is adjustable without an adjustable base made by Vivon (a Zinus brand) and can be seen here http://www.furnituretoday.com/article/530577-Vivon_introduces_new_adjustable_bed_technology_at_Las_Vegas_Market.php however this is not the norm and I would question it’s benefits as you would need to replace the entire system if one part of it broke down.
In general terms, the iComfort is a better mattress than the Novaform gel (it has higher density memory foam about 5lbs) but I believe it is too expensive in comparison to other higher quality memory foam mattresses. The Novaform is probably a better overall value even though the memory foam is lower quality however I also don’t believe it represents a great value either … again when compared to other 4+lb memory foam mattresses which can be purchased for less and use the same or higher quality memory foam.
The zero gravity position that is a preset position on several adjustable bases (Reverie and Ergomotion) or can be set as a custom position on others (Leggett and Platt) certainly does relieve stress on the lumbar and could be a comfortable position for those that sleep on their back for several hours without moving however this if rare. Some degree of movement and shifting of positions is a natural and healthy part of sleep and if someone was sleeping on their back and moved to their side, this position could soon become very uncomfortable (think of sleeping on your side on a reclining chair for example). I personally believe the best reason to sleep in an elevated position is to help deal with reflux type of conditions as the elevation of the torso can help prevent this and the disadvantages of this position are offset by the advantages of preventing reflux which can be very uncomfortable and in some cases even dangerous if it happens when sleeping on your back. Of course a health care professional may also recommend this elevated position for other reasons as well as part of a specific treatment.
I also believe that memory foam is not necessarily a great choice for back conditions for several reasons including the greater difficulty of changing positions, because it softens or hardens with changing temperature which results in changes in alignment during the night, and because it “creeps” over time more than other foams which means that there is a tendency to sink deeper into the mattress (again changing alignment over time). Latex in the right ILD (softness/hardness) offers similar (some believe better) pressure relieving qualities to memory foam without its disadvantages and is more supportive in nature (keeps your spine in better alignment without the same tendency to “change” over the course of the night). It is also a cooler foam for those who tend to sleep hot and keeps its initial qualities and lasts longer than memory foam.
I believe that a good choice for those with back issues would be to use pillows to help with stiffness and improve sleeping alignment. For side sleepers this would mean a pillow between the knees, for back sleepers a pillow under the knees, and for stomach sleepers a pillow under the stomach pelvis area. Examples can be seen here [url=http://createhealthchiropractic.wordpress.com/2007/12/12/poof-pillows/]http://createhealthchiropractic.wordpress.com/2007/12/12/poof-pillows/[/url]. This way it is easier to change positions during the night than having to change the height of an adjustable base. Correct pillows for the head and neck are also important for back issues (head and cervical support for back and side positions and thicker for side, slightly less thick for back, and very thin or no pillow for stomach). Changing positions itself is a natural part of restful sleep and can also be an important part of relieving stiffness.
In general, back stiffness, soreness, and other back issues indicate the importance of sleeping in alignment in all your sleeping positions (not just a single position) and the ease of movement between positions and this alone can often make a big difference if the mattress you are currently sleeping on does not create the best spinal alignment … no matter how seemingly comfortable it may otherwise be.
I personally have a adjustable base (Reverie Deluxe) which I like a lot for watching a movie or reading in bed etc but it was not for health or back reasons and we sleep on it in the flat position only. I would use the zero gravity position for a nap but not for sleeping all night long.
One final comment is that you may have meant the EComfort mattress made by Anatomic Global (which is sold at RC Wiley) which is also a memory foam mattress that is suitable for use on an adjustable base but is not the same mattress as the iComfort gel memory foam which is made by Serta or the Novaform gel memory foam mattress. If this is the case then let me know and I’ll be happy to give you some feedback that is more specific to the EComfort.