Hi espiritone,
While there is no way to make any meaningful comments about the quality of your mattress without knowing what materials are inside it (even if you knew the model) I can make a few comments that may be helpful.
If the law tag is still on the mattress then this may give you a generic idea of the materials in the mattress based on weight.
A warranty has very little to do with the useable life or quality of a mattress because foam softening and the loss of comfort and support that goes with it is the main reason people need to replace a mattress and this is not covered by a warranty. You can read more about warranties in post #174 here.
The durability of a mattress is also relative to the person sleeping on it and the different effect of foam softening and the degrading of materials on different people can mean that a mattress may still be inside the range of one person’s needs and preferences and be well outside the range for someone else. You can read more about durability and how it is relative to each person in post #4 here and the post it links to.
I certainly understand the attraction of a very low price but this mattress could very well be close to the end of its useful life and if that is the case then you could end up paying for it in other ways including your quality of sleep and its effect on your waking life as well. At the very least I would make sure you test it very carefully for PPP (Pressure relief, Posture and alignment, and Personal preferences), inspect it very carefully and be very cautious of all the risks of buying a used mattress, and even then be aware that it may be close to the end of its useful life.
Phoenix