Hi dapps06,
I looked at your pictures and your mattress appears to be less than 11" thick and the Nutrition would be a little bit thicker than 11" because the thickness of the cover and the fire barrier will add some additional thickness to the 11" of latex inside it. The Nature would also be a little more than 10" thick for the same reasons and it “looks like” you have the Nature based on the thickness.
If you remove the cover then you can check the thickness of the top two layers inside inside your mattress and confirm which mattress you have. The top two layers in the Nature would both be 2" thick and with the Nutrition the top layer would be 3" and the middle layer would be 2". You may also be able to see a sticker on the layers that will confirm the ILD of the layers (they are normally at the head end of the bed apparently) although I’m not sure if all of their mattresses would have the sticker.
The PLB mattresses also have a fairly thick fire barrier so your salesperson is correct that there could be some minimal initial impressions as a result of the fire barrier inside the mattress either compressing or perhaps even shifting if it isn’t tightly attached (you can see the fire barrier surrounding the latex when you remove the cover).
It’s also possible that your impressions could be the result of the foundation or support system underneath your mattress and I know some retailers that won’t sell the PLB foundations because they aren’t particularly good quality and the slats aren’t close enough together which can also lead to some sagging underneath the mattress which can also show up on the sleeping surface. You could check this by putting your mattress on the floor and seeing if it makes any difference.
It’s also possible that your grandmother has a previous version of the Nature which would be slightly different from their current model.
It’s not likely that a warranty claim would be approved anyway since their warranty has a .75" exclusion and impressions that are less than that aren’t considered to be a defect in the mattress.
There will also be a break in and adjustment period with any new mattress (see post #3 here) and it’s also possible (and perhaps the most likely possibility of all) that the Nature just isn’t a good “match” for you in terms of PPP (Posture and alignment, Pressure relief, and your personal preferences).
I’m not sure how long your trial period is but if you are still experiencing discomfort or pain after a few more weeks of sleeping on the mattress and none of the suggestions makes a difference then the most likely cause of your discomfort is that the mattress is just the wrong “fit” and I would consider a comfort exchange.
If you do decide to keep the mattress (and since the cost of a trial period was built into the price of your mattress I would only do so if you are sleeping well on it) and the visible impressions get any deeper and are more than .75" then you would have a valid warranty claim and you could replace the mattress although I would also agree with your retailer that this also isn’t likely to happen because of the durability of the latex.
Phoenix