Hi ananee,
Welcome to the Mattress Forum! 
Yes, the major brands such as Sealy/Stearns & Foster, Simmons, and Serta (some of which are offered at the store you visited) all tend to use lower quality and less durable materials in their mattresses than most of their smaller competitors that will tend to soften or break down prematurely relative to the price you pay which is why I would generally suggest avoiding all of them completely (along with the major retailers that focus on them as well) regardless of how they may feel in a showroom along with any mattress where you aren’t able to find out the type and quality/durability of the materials inside it (see the guidelines here along with post #3 here and post #12 here and post #404 here).
Endless Comfort isn’t a member here of the site, but is listed as an option that might offer products using higher quality materials that may be worthy of consideration in your area.
I too noticed that the web site isn’t live any more, but the company seems to be producing mattresses. I’m not personally familiar with the ownership of this company, but the main source for any mattress layer information would be your local retailer as opposed to contacting the factory direct, as the factory is not normally equipped to handle direct consumer questions. I did pull up an old link for their facility here with some information, but I don’t know if this is still accurate, as the web link is not live. There is an Endless Comfort Bedding with a different address listed here, but with the same phone number. You may wish to phone them if you’re not able to find the information listed here from your local retailer.
I’ll be interested in learning if you are able to get specifications of any mattress in which you are interested (unfortunately the mattressmart.ca site doesn’t list any meaningful specifications on the Endless Comfort models), or if you are able to contact Endless Comfort directly.
Phoenix