Here are some tips for you. Consider if your Sealy is a pillow top, or a "firm" non pillow top model. That will help you narrow down the choices to select from.
Be sure to purchase the foundation (formerly known as box spring) with the mattress as a "set". Big mistake is thinking you can use the one you have, that it is still good. Never the case. Plus warranty will be cut or voided if you don't buy in a set.
Stearns and Foster is from the same parent company as Sealy. So if you want a top of the line Sealy, you may want to check out the Stearns and Fosters as well.
Don't be shy about getting comfortable on the model in the store. Take your time and get into your favorite sleep position. It will give you a better idea of how the mattress is supporting your body and its pressure points.
Of all pieces of furniture, the mattress is the one thing that people tend to put off replacing long after it has lived its life span. People will replace sofas far more easily and quickly than a mattress. Yet, your whole physical well being depends on how your body is being supported through the night. You really will spend a third of your life on those mattresses..
Neotiate. Things like a free bed frame, delivery charge, removal of old bedding, are often negotiable. Don't be shy about asking.
Good luck and happy shopping!