Hi ScottBraun,
Welcome to the Mattress Forum! 
Spindle uses three 3" layers of continuous pour natural Dunlop from Mountain Top. All three of the layers of medium and firm may be arranged in various configurations to create 4 plushness levels from soft to extra firm.
The UD Total Latex uses a 6" Talalay core (can also be had as 32 ILD natural Dunlop core). The top 3" layer can be changed out in different plushness levels of Talalay.
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fort exchange/returns: Spindle has a fee if returned and DreamFoam is free
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Spindle does not build in exchange/return fees into the cost of their mattress. They do allow one layer adjustment within the firsts 365 days for a flat $200 fee, and you get to keep the original layer. If you decide you don’t like the mattress, they do allow you to donate it within 365 days for a refund less $199.99.
Dreamfoam does have a layer exchange program for a $200 fee (which is refunded), and they have a 120 night trial policy where you may receive a full refund.
Spindle uses a zippered cover using organic cotton quilted to eco-wool.
Dreamfoam uses a bamboo knit cover with organic wool and a thin layer of polyfoam underneath.
I think that just about every person who buys a mattress or is a member of the forum has wrestled with a similar scenario which is all about how to choose between “good and good” choices. At this point, it’s time for me to step out of the way and I don’t think anyone can or even should tell you what to choose at this point but some guidance in how to choose may be helpful.
The bad news is that even with good or great mattresses to choose between final choices are not always easy to make, especially when it involves a combination of objective, subjective, and intangible factors that can be difficult to attach a “value” to or when the differences in “value” between them seems very small. The good news is that any of your choices are better than what the large majority of people end up purchasing and in terms of quality and value there are really no “bad choices” or “mistakes” left any more and when you are at this point and there are no clear winners between your finalists then the odds are high that any one of them would be a good choice that you would be happy with.
Both Spindle and Dreamfoam are members of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex and different configurations, and I would not hesitate to recommend them for your consideration.
Phoenix