Hi Polyphasicsleep,
I know it’s not related to your questions but I noticed your username and there is a great website here about polyphasic and free running sleep that may be of interest to you (although you may already be aware of it).
As far as your mattress search … the first place I would start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress that is the best “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for that are involved in each of them and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability, durability, and value.
You can read some of my thoughts about Essentia and some of the misleading claims they make and some forum discussions with them in this thread and this thread and posts #3 and #4 here). Needless to say I would be very cautious here and make sure you make some very careful value comparisons with other mattresses that are available to you.
The better options or possibilities I’m aware of in the Quebec City area (subject to the quality/value guidelines I linked) are listed in post #276 here.
Phoenix