Hi PeterKKB,
Thanks for providing the links to your two mattress finalists manufactured by the UK based company Naturalmat.
Based on your criteria you are in the fortunate position that both would likely be a suitable choice with no weak links in terms of durability and great in terms of temperature regulation. From your previous description, I was a bit concerned about the use of recycled cotton in a mattress but the denim used in their mattress filling is thoroughly cleaned, shredded, and futher processed using noninvasive methods.
Generally, cotton and various cellulosic fibers are more cooling than synthetic fibers and my note regarding cotton was more connected to possible “clamminess” and humidity, which are certainly related to temperature regulation. While cotton is a more temperature neutral material it may feel clammy or humid when saturated but in the case of Splendid Spring, the denim is used in combination and placed under a layer of lamb’s wool which has the ability wick away and to store moisture into its fiber. Additionally, the wool layer is closer to your body and any moisture absorbed by the cotton mattress cover will be “transferred” to the lamb’s wool layer thus reducing the feeling of clamminess. All in all, it is still a great combination for wicking moisture away. The Sumptuous Spring option may give you slightly more of a cooling effect due to a little more air circulation but it is also double the price of the Splendid Spring. Both mattresses are well designed and use good/quality materials. The company is environmentally aware and using natural biodegradable components and sourcing their materials based on Fair Trade principles
Your choice between “good and good” would depend on all the criteria of your personal value equation that were most important to you as outlined in post #2 here and can be helpful to revisit and perhaps a more detailed conversations about each of their 2 products you are considering, your confidence about PPP and the suitability of each one, their prices, your preferences for different types of materials, the options you have after the purchase to fine-tune the mattress or exchange or return the mattress, any additional extras that are part of each purchase, and on "informed best judgment.
I look forward to hearing back about your final decision and any other questions that you may have.
Phoenix