New person here. Very helpful site. Am studying tutorial but a lot to absorb. Severe arthritis has turned my Beautyrest Black into a nightmare. Recently slept on soft beds while traveling - heaven. Always thought extra firm would keep back problems at bay but I hurt all over and hardly sleep > 4 hrs. Looking to buy BME soft but worried about lower back. Any comments would be appreciated. Will go back & study tutorial now. Thanks
Hi isosleep,
Welcome to the Mattress Forum! 
I’m sorry to hear about your arthritis and pain with your current mattress.
Unfortunately, there is no specific configuration or type of mattress that is “good for arthritis” in general because each person is unique, and a mattress that works well for one person with a specific condition such as arthritis 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 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.
A forum search on fibromyalgia (you can just click the link) will also bring up more comments and feedback from others that are in similar circumstances (fibromyalgia and arthritis sufferers tend to respond to similar pressure-relieving configurations) that may be helpful (but it will also confirm that there isn’t a single “best” combination of materials that will work for everyone in your situation).
Nothing can replace your own personal testing, as you do have some specific health considerations. You’d obviously want to consider something that allows for enough surface comfort while sleeping upon your side and back, and also assists with pressure point relief, while still overall being resilient enough and provide enough support while sleeping. Overall, the two basic functions of a mattress are to support and to provide comfort (you can read more about that here if you like), with alignment being the first priority and then comfort coming second, but in your case having adequate comfort and pressure point relief will be quite important.
In general … what you would be looking for is a mattress with firm enough deep support and then comfort layers that are “enough” in terms of thickness and softness to “fill in” and support the more recessed parts of your sleeping profile and relieve pressure in your most pressure prone sleeping position (usually side sleeping for those who sleep in this position) so that there is less risk to alignment in your other sleeping positions. You didn’t list your BMI, but generally the BME offers enough deep support for most individuals in a more “normal” BMI range.
There is no one firmness level that is “best” in general because it would depend on the body type, sleeping style, and individual preferences of the person. A mattress needs to have deeper layers that are “firm enough” to stop the heavier parts of your body from sinking down too far and make sure you sleep with your spine and joints in good alignment and upper layers that are thick and soft enough to “allow” any pressure points such as the hips and shoulders to sink down far enough to relieve pressure points in all your sleeping positions as well but “firm enough” and “soft enough” can vary widely from person to person. In your situation, it seems that you have discovered that you need a bit more plushness than your current mattress offers.
There is also more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel” although this may be more than you really need to know to choose a mattress that is a good “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences).
There is some information about the many different symptoms that people may experience on a mattress and some of the most common causes behind them in post #2 here that may be helpful.
I know I’ve added to your reading list, but hopefully this gives you a bit more direction as you search.
Phoenix