Hi eliminator23,
You can see my comments about Ton furniture in post #1 here. My conversations with them certainly indicate that they are knowledgeable about mattresses and materials.
In a base layer … 1.8 lb polyfoam is usually fine and would be the minimum density I would consider to be acceptable unless you were in a very low budget range. The density range of polyfoam is lower than the density range of either memory foam or latex. Density is not connected to firmness and any density polyfoam can be made in any firmness level. Density is the biggest factor in quality and durability. In other words 2.2 lb polyfoam would be more durable than 1.8 lb polyfoam but would typically be more costly as well.
The support layer of a mattress is not typically the weak link of a mattress though so I would consider 1.9 lb polyfoam to be perfectly acceptable. 2.2 lb would be good quality polyfoam (equivalent to what Tempurpedic uses in the base layers of their mattresses). If you are heavier or the top layers are thinner in the range of 2-3" or less (which would mean the base layer would be more subject to the mechanical forces of repeated compression) … then polyfoam density in the 2 lb range or higher would be better yet.
I would not put a lot of emphasis on warranties because the biggest issue in a mattress is foam softening and the loss of comfort and support which is not covered by warranties. In other words … warranties have little to do with how long a mattress will last for any particular person. Knowing that the materials in a mattress are high quality … particularly in the upper comfort layers which are the weak link of most mattresses … is a much more reliable indicator of the durability of a mattress than the warranty. You can read more about mattress warranties in post #174 here.
Phoenix