Hi Redsaffron,
They both use Dunlop Latex in their mattresses but Spindle has the option of either synthetic Dunlop or 100% natural Dunlop that is made with a continuous pour process and Cozy Pure uses 100% natural Dunlop that is made in a mold (Note: Spindle is now only using 100% natural continuous pour Dunlop in their mattresses). 100% natural Dunlop that is made in a mold or made with a continuous pour process would be very comparable in terms of quality and durability. There is also a difference between the designs of each mattress, the type and quality of the covers they use, the additional benefits of buying from each one, and like any two business there would also be other differences between them and their business models and policies that would also affect their prices (see post #14 here).
When you are down to final choices between “good and good”, none of them have any weak links in their design, and if there are no clear winners between them, then which one would be the best choice for you would depend on all the objective, subjective, and intangible parts of your personal value equation that are part of each mattress purchase that are most important to you (see post #2 here).
Phoenix