Hi Mikew096,
Welcome to the Mattress Forum! 
I don’t keep track of sales for the most part mainly because the better manufacturers don’t need to use them to sell good quality and value mattresses and sell at a “regular” price every day of the year. It would also be an overwhelming job to keep up to date on sale prices that just change their name. Better retailers and manufacturers tend to sell at the same prices every day of the year with some sales with smaller discounts on occasion for legitimate reasons. Most sales in the mattress industry are “fake” and based on inflated prices. I treat them more as a warning sign than as a benefit … at least for the most part.
Post #1 here has a step by step process that will greatly increase your odds of finding the best possible quality and value mattress available to you locally that will fit your specific needs and preferences. If for some reason there is little available to you locally that has the kind of quality and value that you want … then the greater risk of an online purchase that you can’t test first can make sense. some of the better choices for online memory foam mattresses are listed in post 12 here.
With any mattress purchase … the only way to know the quality, durability, and relative value of a mattress is to work with a manufacturer or retailer that will give you the details of all the layers in a mattress you are considering so you can make meaningful comparisons with other similar mattresses. Who you buy from and their knowledge, experience, and ability to “fit” you to a mattresses based on your body type, sleeping position, and other preferences can be even more important than what you buy. You can’t “feel” quality in a mattress and low quality and higher quality materials can feel and perform the same in the short term. On the3other hand … even the highest quality mattress may be completely unsuitable for your specific needs and preferences. Being armed with some information about how to tell good quality from bad and having some sense of the type of mattress that may work best for you or that you are most interested in trying is always a good idea before you begin testing mattresses.
As with any mattress … knowing the quality of the materials is the only way to know the quality/value. I would not consider any mattress that used 3 lb memory foam unless you were using it for a guest bed or were planning to use it for the short term only. I would also want to know the density of the base foam.
As a general guideline …
Comfort/Pressure relief is what you feel when you first lie on a mattress. This is mostly about the comfort layers.
Support/Spinal alignment is what you feel when you wake up in the morning (either with or without back pain). This is mostly about the firmness of the support layers in combination with the thickness of the comfort layers and how well the layering matches your body type and sleeping positions.
durability/quality is what you will feel a year or more down the road and can only be determined by knowing the quality of the materials in the mattress. Lower quality materials will soften and degrade faster and the loss of comfort and support isn’t covered by any warranty.
The guidelines I would use to make meaningful comparisons between memory foam mattresses are in post #10 here.
Phoenix