Hi soreneck,
Welcome to the Mattress Forum! … and I’m glad you found us 
Hopefully you’ve had the chance to read the mattress shopping tutorial here which includes most of the basic information, steps, and guidelines you will need to make the best possible choice … and know how and why to avoid the worst ones.
A pillowtop is easy to identify because it’s a method of construction that has a separate “pillow” that is sewn to the mattress with recessed edges (like this) and is just a method of construction that allows the top layer in the “pillow” to respond more independently. The problem with most pillowtops that are sold by the major brands or in the mainstream industry isn’t so much the pillowtop design itself as the quality/density and durability of the materials inside it.
There is more about the three most important parts of the “value” of a mattress purchase in post #13 here and #2 is to make sure that you can find out the type and quality of the materials in your mattress (see this article) so you can compare them to the quality/durability guidelines here … or post them on the forum where I’d be happy to make some comments about the quality and durability of the materials inside a mattress. This is always the most reliable way to make sure you are making a durable choice no matter what type of construction a mattress uses.
If for any reason you aren’t able to find out the specific information you need to know to make an informed purchase decision then I would pass the mattress by (see the guidelines here).
There is more information in the foundation post here about the types of support systems that generally work best for different types of mattresses.
Corsicana in general tends to specialize in lower budget or “promotional” mattresses but like most manufacturers they make a very wide range of mattresses in different budget ranges. In terms of quality and durability, any specific mattress is only as good as its construction and the type and quality of the materials inside it regardless of the name of the manufacturer. If you can provide the information in the article I linked and list it on the forum I’d certainly be happy to make some comments about the quality/durability of the materials in the particular Corsicana mattress you are looking at.
The better options and possibilities I’m aware of in the Eugene area (subject to the quality/value guidelines I linked) are listed in post #2 here. I took a quick look at the retailers you listed and updated the list and included the manufacturers they carry where your odds are higher that you will be able to find out the information you need about the type and quality of the materials inside their mattresses to make an informed choice.
Phoenix