Hi debating,
Once again … the only way to know the level of formaldehyde or any specific VOC’s in any material or mattress is based on seeing the lab testing results. All you can know for certain is whether it is under the testing limits for any certification that it has.
The most important part of the “value” of a mattress purchase is how well it matches your unique needs and preferences in terms of “comfort” and PPP (Posture and alignment, Pressure relief, and Personal preferences). No matter what the quality or price of a mattress or how long it will last … if it’s not a good match for you and you don’t sleep well on the mattress it would have little value to you.
Outside of PPP … the most important part of the value of a mattress purchase is durability which is all about how long you will sleep well on a mattress. This is the part of your research that you can’t “feel” and assessing the durability and useful life of a mattress depends on knowing the type and quality of all the materials inside it regardless of the name of the manufacturer on the label so I would always make sure that you are able to find out the information listed here so you can compare the materials and components in a mattress to the quality/durability guidelines here so you can confirm that there are no lower quality materials or obvious weak links in a mattress that would compromise the durability and useful life of a mattress before making any purchase.
A warranty is important to guard against manufacturing defects in the materials or components inside a mattress that can happen on rare occasions but I would also keep in mind that mattress warranties only cover manufacturing defects and they don’t cover the gradual (or more rapid in the case of lower quality comfort layers) loss of comfort and support that comes from foam softening that is the main reason that most people will need to replace their mattress. In other words warranties have little to do with the durability or useful life of a mattress or how long it may be until you need to buy a new mattress. If there is an actual defect in the materials it will usually show up early in the life of the mattress but knowing the quality and durability of the materials in your mattress is always a much more reliable way to assess the durability and useful life of a mattress than the length of a warranty. There is more about mattress warranties in post #174 here.
There is also more about the Dormeo Octaspring mattresses in this topic and in this topic and a forum search on Dormeo and on Octaspring will bring up more comments and feedback about them as well.
Phoenix