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Your situation is a bit more complex as you have a higher BMI = 31.7 kg/m2 and also “very sensitive pressure points”. Because I don’t know how much you perused our site since you found TMU (The Mattress Underground) I’d first make sure you covered some of the basics needed before you start any DIY so that you have realistic expectations and that you are comfortable with the learning curve, uncertainty, trial and error, or in some cases the higher costs that may be involved in the DIY process. We have several DIY experts on TMU but it seems you may need to do a bit more legwork before reaching out for guidance.
And now down to the basics… What type of DIY do you have in mind? (hybrid, all latex, foam combo, etc.) What are the materials you prefer in your mattress? What is your history with previous mattresses? Do you have any other health conditions that might affect the quality of your sleep? To start off and before answering these questions, I’d read some of general information in the mattresses section of the site (particularly in the sections about sleeping style, preferences, and statistics along with putting the layers together and the page on tips and tricks here ) that can give you some general concepts, guidelines, and insights about the effects of different body types, sleeping styles, and mattress designs for different people but this is only generic and not specific to any particular person and may be more complex than you really need to know.
Unfortunately, there is no specific configuration or type of materials that are “good for pressure point relief” because each person is unique, and a construction that works well for one person with a specific condition or sensitivity may be completely unsuitable for someone else with the same conditions to sleep on. In very general terms, softer and more pressure relieving materials that provide a more “relaxed” sleeping surface will tend to work better than firmer materials because for most people with pressure points issues or fibromyalgia or arthritis a softer more pressure-relieving sleeping surface is a more important priority, but I know that this does vary with individuals, as well as varying day-to-day. (For example, latex and memory foam have been popular combinations for this application and have been mentioned over time here on the forum, but again everyone is different.)
A forum search on fibromyalgia (you can just click the link) will also bring up more comments and feedback from others with pressure point issues that may be helpful (but it will also confirm that there isn’t a single “best” combination of materials that will work for everyone with these issues).
As you’re going through your readings, be sure to take a few minutes and browse through the Mattress Shopping Tutorial which includes all the basic information, steps, and guidelines that can help you make the best possible choice.
Once you have a chance to peruse through these readings feel free to get back to us with clarifications and additional questions.