Hi azngeek,
Welcome … and I’m glad you found us 
The Dreamfoam mattress uses 1.5 lb polyfoam in the support core of the mattress (not 1.0 lb).
You can see some comments about the quality/density of the materials and the durability of this mattress in post #3 here and there are also some comments about the small percentage of reviews that mention sagging in post #2 here that should be helpful.
You are at the border of the weight range where 1.5 lb polyfoam would still be a suitable choice (in this budget range especially) and would probably have a relatively small effect on the durability and useful life of the mattress although it would have “some” effect compared to those that are in a lighter weight range.
When you can’t test a mattress in person then I would make sure you talk with them on the phone about your firmness choice because the most reliable source of guidance is always a more detailed conversation on the phone with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs to different body types, sleeping positions, and preferences (or even to other mattresses that they happen to be familiar with) than anyone else.
Just in case you weren’t aware of it as well … if you purchase a Dreamfoam mattress directly from the Dreamfoam site instead of Amazon then there is an additional 10% discount and you would also have the benefit of their 45 day comfort guarantee as well.
Phoenix