First I want to say I am so glad I stumbled upon this website before making my first memory foam purchase. Phoenix has really helped guide me away from what I should NOT buy so thank you for that!
My wife and I decided to give Luxi Sleep a try. We got our mattress 3 nights ago and are in absolute LOVE with the mattress. We got a good deal on this ($1050 for the King after $200 holiday coupon and $50 rebate as they were a bit slower than expected to ship). My wife is light (5’ 2" and weighs only 105 lbs) and I am fairly heavy (5’ 10" and 240 lbs). My weight fluctuates a lot but has been more on the lower end. I have been 300 lb+ for a while but have been stable in the 210-240 lb range for a while now. I realize lower weight = longer longevity for memory foam and any mattress for that matter which is a big motivator for me to keep the weight off 
Ok off to my question. So right now my wife prefers the medium setting. Me, probably because of my weight, prefer the firmest setting because I feel the medium setting sinks in/hugs a bit too much for me. On top of that I am a stomach sleeper so I REALLY need all the support I can get. Before I get into my question I wanted to point out the mattress composition directly from Luxi FAQ:
3 1/2 inch SBT Layer - A proprietary 4 lb. Density foam architecture that offers air flow and resists sagging and body impressions.
1 inch Memory Foam Layer – 4 lb. Density Visco Elastic Foam
1 1/2 inch Latex Layer - 4 lb. Dunlop Process, 100% Latex (20% Natural/80% Synthetic)
3 1/2 inch Foam Base Layer – 2 lb. High Density Support Foam
3/4 inch Quilt Loft – Quilt Foam and 1oz. Fire Resistant Fiber Fill
So for this, the “Medium setting” in order from top to bottom is: 1.5" Latex, 1" Memory Foam, 3.5" SBT Foam, 3.5" Base Foam.
The “Soft setting” is 3.5" SBT foam, 1" Memory Foam, 1.5" Latex, 3.5" Base Foam.
For the “Firm setting” it can be either: 3,5" Base Foam, 3.5" SBT Foam, 1" Memory Foam, 1.5" Latex
OR
3.5" Base Foam, 1.5" Latex, 1" Memory Foam, 3.5" SBT Foam.
I’m not sure if there are any firmness differences between the two of those “firm” settings but I assumed having the Latex + Memory foam on top of the SBT foam would be the firmest setting (based on the Medium vs Soft settings) and I also preferred this setting as Latex was the 2nd layer and still gave a tiny bounce because of this.
Long story short, I am a bit concerned with this “firm” setting. In terms of support it is PERFECT. I love the feel. However I am concerned about longevity. The other 3 layers are fine, being 4 lbs density. However I’m concerned that in order to make this “firm” my top layer is only 2 lbs in density. Am I correct in my concern? Will this top layer give out/compress much faster than if I had this in the medium setting? I figured it would be cheap to replace this if needed, but I also feel like I can prevent having the “firm” give way/sag quickly by just sleeping on the Medium setting. What are your thoughts? Am I correct in this assumption? Or is the “firm” feel because of the support by the other 3 layers of 4 lb foam enough to compensate for this compression (and therefore maybe it won’t break down as quickly as I think it would)?
I figured Luxi Sleep probably thought of this but also probably assumed most people would prefer a Medium or Soft setting and didn’t think it would be a big issue…maybe I’m wrong? I emailed their support for advice. I know they provide advice if someone weighs >250 or >300 lbs (I think someone mentioned they also provide a topper for that? Not sure…). I’m not >250 but 240 lbs is right on that cusp so I want to make sure this mattress lasts us at least 8 years!
Thanks for the help!
EDIT: I should add, I read the FAQ you have about the foundation support underneath the mattress. I spoke with luxi and they confirmed for me they have no preference and said I can either reuse an existing box spring or leave the mattress on a flat support. Their warranty covers either. I currently have an existing 5 year old “active” box spring. However as far as I can tell it seems to not sag and have a LOT of support (it is a posturpedic sealy box spring I believe). I’m wondering if this should be alright and whether having the SBT foam layer on the bottom (with the columns facing down) would affect longevity/feel?
Also for those curious some more on the SBT technology from their FAQ (I post this because I am still unsure as to whether or not the SBT technology will provide the same longevity as a 4 lb memory foam layer would…also concerns about this being a “Support” layer for the firm setting):
Support Balancing Technology is a fabricated enhanced stability viscos foam layer that offers cushioning and support simultaneously for the higher pressure body regions, such as hips, shoulders, etc., so that the body is in alignment during sleep. In particular this layer of pedestal-shaped foam offers support, softness control, airflow and minimal motion transfer like no other foam on the market. While it is not a memory foam layer in the usual consumer sense, it is derived from that chemistry and presents as a faster responding, more stable and durable viscos elastic foam.
This is a patent pending technology
PODS DURABILITY: This foam is made of a very durable foam and through our testing we have had no problems.There is both horizontal and lateral movement in the pods. This method of using pods and breaking up the surface is actually more durable than just a block of foam. It creates a soft feel or sensation and when weight is applied the bottom of the T shape actually becomes stronger and therefore prevents hammocking in the mattress. This is where the real engineering & design work come into play.
BUCKLING: The buckling columns (or the Pods) act as coils. So you get the same benefit as a spring but you just get better technology with the SBT for support and body alignment
EDGE SUPPORT: The SBT element ends up delivering a degree of edge support unlike most memory foam mattresses. When you sit on the edge of the Luxi the buckling column collapses under your seat, away from the edge about four inches, so you sink back instead of forward. Care has also been taken to insure that no matter what the mattress size, that the SBT layer always has a row of the supportive pedestals right at the edge of the mattress, whether it’s a twin, twin XL, full, queen, king, or California king. They have done a good job with the computer modeling to get each size just right at the edge.