Hi Gormeroth.
Welcome to our Mattress Forum!
Thank you for sharing your sleep statistics with us, as well as your history of back pain due to the gym injury. It must be unsettling to deal with on an ongoing basis for 8 years now and having it exacerbated by a “cheapo bed”.
As you’ve been doing some good research and found some solutions let’s “jump forward” to your second post and then loop back to any lingering questions from your original post.
You mentioned you’re getting your components from Sleep EZ. They are a Trusted Member of our site, we think very highly of them, their products, and their expertise in DIY mattresses!
While both of the configurations you are considering look adequate in terms of longevity and the feel you are looking for I’d pause and look a bit deeper into how this thickness and layering arrangement can be suitable for your sleeping positions, chronic back pains, and BMI, The density of the top memory foam layer is adequate for your BMI so It looks like you’ve read our Mattress Durability Guidelines already.
I’d be interested to know what guidelines you are using to come up with either of your configurations. Is this something you’ve constructed based on mattresses you’ve tested that you like, that you’re attempting to replicate? have you had any conversations with Sleep EZ regarding your specific needs/sleeping statistics?
As you suffer from lower back pain and you are primarily a side sleeper, I’d hesitate to use 6" thickness of comfort layers. Some cushiness will be also borrowed (secondary comfort/softness) from the 3" medium firmness third layer under as well. Given your chronic lower back pains, you’d need adequate support to maintain neutral spinal alignment, while also meeting your comfort needs. In general, a good starting point for a basic comfort layer for a side sleeper is 3". Then depending on weight, body shape, preferences, and the firmness of the support layers, go up or down from there. Most side sleepers will fall in the range of from 2" -4".
As you are buying layers from Sleep EZ I can’t recommend highly enough that you reach out to them and explain what you want to achieve and inform them of your condition so that they can guide you of what construction layer works best for you as they are much more familiar with their own materials and how they interact within a particular build than anyone else and they can use the information you provide them about your body type and sleeping positions, your preferences, your history on different mattresses, and the results of your local testing to make suggestions based on the “averages” of other customers that may be similar to you. Sleep EZ has a dedicated mattress expert forum on TMU where you can ask for support and they are extremely customer-oriented.
That said, the benefit of a DIY mattress is that if a layer isn’t working for you, it’s very easy to remove it or replace it with something else to fine-tune comfort/support to your needs.
To address your question regarding mattress encasements from your original post…First off, I’d hold off with purchasing one until the DIY layering is as close as possible to your needs and preferences. This is because you may find that the perfect layering combo for you is less than 12" and you probably won’t be able to return the encasement. I’d recommend that whatever direction you chose to go that you sleep on it for enough time so that you make sure that you are happy with the final construction.
I don’t have any personal experience with the tempurpedic mattress replacement cover, but as @ebs mentioned, most likely you can find many other similar products. As you seem to love the feel of the tempurpedic encasements, I do not see any reason not to purchase one that would fit your DIY construction. You will, of course, want to make sure it is large enough to fit all of your layers once you finalized your construction.
Looking forward to hearing more details about the project progresses. Good Luck!
Phoenix
@ebs Thanks for chiming in, great insights for a first-time poster!