Hi Winnie,
In the post I mentioned earlier as a starting point (linked in my signature) … there is a link to these guidelines and #1 in the guidelines is …
1. Avoid buying a mattress made by any of the major national brands such as Sealy, Simmons, Serta, Tempurpedic. While they are not all “bad” mattresses and some may even be good quality, … none of them have good value when compared to similar mattresses made by smaller independent manufacturers. NONE
Hopefully this answers whether I think you should buy a Sealy 
There is more information about the Optimum line in post #48 here if you want more information but i would avoid them … and any salespeople who were promoting them.
When a salesperson who is promoting this type of mattress tries to tell you the mattress is good quality (or if you ask them) … then just ask them to tell you the details of every layer in the mattress including the density of any memory foam and polyfoam in the mattress. Of course they won’t know which means that for them “quality” is a meaningless word because the only way to know the quality and value of a mattress is to know the details (including foam density) of every layer of a mattress.
Who you buy from and their level of knowledge and experience (not just marketing training that tells the stories they are told to sell) can be one of the most important parts of successful mattress shopping.
I would just follow the steps listed in the post and never consider any mattress where you can’t find out what is in every layer inside it … no matter where you are buying from.
Phoenix