Hi leslie7622.
Welcome to our Mattress Forum. 
I double-checked and the Nest Bedding code “Nestlove” is valid for a 10% discount until Feb 1, 2021, and is not stackable, The TMU9 is the default discount code which should work when no site sales are in effect.
It is possible that the difference in comfort you are experiencing is caused by more “breaking-in” from customer use in one showroom than the same model in a different store (provided you tried the same firmness)
The Alexander Signature Hybrid (Firm) doesn’t use latex with the following layer breakdown:
Reinforced Polyester Encasement
.5" 4 lb. Luxury Memory Foam, Quilted Thermic Phase Change Top
3" 3.5 lb. - 4 lb. TitanChil Endurance Foam®
1" 3 lb. SmartFlow Support Foam
8" Quantum Edge Pocketed Support Coils
1" 3 lb. Base Support Foam
The (12.5") Natural Hybrid Latex (Firm):
.1" Organic Stretch Knit Cotton and Joma Wool
1.5" 1.5lb Eco Flex Quilting Foam
3" 100% NR Dunlop Latex 34 ILD
1" 1.5LB Eco-Friendly Comfort Foam
6" Caliber Edge Coil Support Pocketed Coils 16 gauge steel
1" 1.5lb Support Foam
The 28 ILD is for Medium firmness. I’d first verify that the beds you tested for the Hybrid Latex in both shops are the firm option to help you make your best decision.
It’s not a surprise that the feel of the Hybrid latex mattresses is noticeably different than the Hybrid Signature, especially given their varied material compositions. Although I do personally like the feel and properties of latex, the choice of materials is a personal preference. For example, there are many people that prefer a Memory Foam feel and are “used” to it to such a degree that any change to a different material may be perceived as very uncomfortable. There is absolutely nothing wrong with using Memory Foam or Polyfoam in a mattress… provided that it meets durability guidelines here . The best way to know which types of materials or mattresses or firmness levels you tend to prefer in very general terms will be based on your own local testing and your own personal experience.
I’d also make sure to have a look at the differences between latex and other types of foam in Post #2 here for latex vs memory foam comparison and in Post #2 here which has some pros and cons of latex vs polyfoam.
Good luck and let us know which one is your finalist!
Phoenix