They make it really hard but it's definitely possible to compare. At least in the Beautyrests, it's easy to find the thickness and a breakdown of the layers in a particular mattress. Example-
http://www.mattressfirm.com/Simmons_...ress-P335.aspx
SPECS:
• Comfort Type: Medium Soft Plush
• Upholstery: 1/2" TruTemp™ Gel, 2" AirCool® Memory Foam
• Quilt: 1" AirCool® Foam, 1 1/4" AirFeel® Foam
• Construction: AirCool® Mesh Border, Ventilated AirCool® BeautyEdge® Foam Encasement, 1/2" Energy Foam
• Foundation: Triton® Foundation
A quick Amazon search brings up this:
http://www.amazon.com/Beautyrest-Rec...st+13%22+plush
Model Name: Manorville
Comfort Level: Plush
Mattress Crown Height: 13.5"
Mattress Border Height: 11.0"
COMFORT LAYERS: Foam Layers in a mattress that help create the comfort level (ie. Firm, Plush or Pillow Top)
Quilt Layers: Layers of Fiber or Foam sewn to the cover of the mattress
First Layer: FR Fiber
Second Layer: 1.25" AirFeel Foam
Third Layer: 1" AirCool Foam
Deck Layers: Layers of Foam located in the "pillow top" of the mattress
First Layer: N/A
Upholstery Layers: Any layers of Foam in the mattress that lay on top of the support layer
First Layer: 1/2" TruTemp Gel
Second Layer: 2" AirCool Memory Foam
Third Layer: N/A
It's clear that they're the same mattress, go elsewhere if the salesman gives you shit about price matching. We saved $800 on our last one with a little bit of internet detective work.