Hi MiniLes,
The first suggestion I would have is to completely reset “how” you are looking for a mattress because you are heading in a direction that will not only confuse you with specs that you won’t know how to “translate”, specs you need to know that are missing, or meaningless or irrelevant information and you will also likely end up with making a poor quality/value choice.
The first place I would start is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you make the best possible choice … and know how and why to avoid the worst ones.
Some of the most important links in the tutorial post that I would make sure you read include …
Post #2 here about the two ways to choose a mattress that is suitable for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences).
The guidelines here and this article about the information you will need to know about any mattress you are considering to make an informed choice and the quality/durability guidelines here so that you can confirm there are no weak links in a mattress and make more meaningful comparisons between different mattresses.
Post #13 here about the most important parts of the “value” of a mattress purchase.
If you are committed to a memory foam mattress then I would be especially careful in such a very low budget range because most of your options would use lower quality materials that can soften or break down much too quickly (sometimes within months) and you can lose the comfort and support that is the reason you purchased the mattress in the first place. For example both of the Sleep Innovations mattresses you are considering use 3 lb memory foam which is a lower quality material than I would consider (unless the mattress is for a guest room or for short term use).
The Dorel Signature Sleep is also a Chinese import (see post #6 here) and based on their shipping weight and using it to approximate foam densities I would also suspect that they aren’t using 4 lb memory foam because the weights just don’t add up. For example using the queen size a 4" layer of 4 lb memory foam would weigh 44.4 lbs. The mattress itself is listed as weighing 68.2 lbs and not even taking the weight of the cover into account … this would mean that the 8" base polyfoam layer only weighs 23.8 lbs which means it would have a density of about 1.0 lb/ft3 which would be an exceptionally low quality material. If the listed mattress weight is correct it’s much more likely that the memory foam is a lower density which would also mean it was less than 4 lb density and below the guidelines I would suggest considering. Signature Sleep also isn’t listed in the CertiPur list here* which means that it doesn’t meet the guidelines I would use on 2 counts (foam quality/density too low and an import that isn’t CertiPur certified) which means I would avoid it completely as well. I would focus on much more reputable and reliable companies that have better quality and value mattresses available.
ADMIN NOTE: *Removed 404 link|Archived Footprint: certipur.us/pages/for-consumers/find-products/
Some of the lower budget memory foam and polyfoam manufacturers I would consider are listed in post #4 here.
I would also read the replies in this topic to another member that is also looking for a memory foam mattress in a very low budget range as well which would be very relevant to your situation as well.
Phoenix