Hi MeJane,
Symbol is the 12th largest mattress manufacturer in the country (see this article) and post #5 here has some thoughts about them as well.
You may find that it’s easier to find out the information you need (see this article) about their specialty mattresses that have latex or memory foam comfort layers than their “regular” mattresses and knowing the quality of the material inside any mattress you are considering is the only way to identify any possible weak links in a mattress and make meaningful comparisons to other mattresses. Before you go to any store to test specific mattresses I would always make sure that you call first to find out what types of mattresses they have on their floor and confirm that you will be able to find out the information you need to make an informed decision about any of the mattresses you want to test or you may end up wasting a trip.
Phoenix