Hi Jamesmattress,
Welcome to the Mattress Forum! 
I’m sorry to hear about your bursitis issue. I know that can be quite painful and make it difficult to find comfortable sleep, as is evidence by your many different mattress purchases.
Unfortunately, there is no specific configuration or type of mattress that is “good for bursitis” in general because each person is unique, and a mattress that works well for one person with a specific condition such as bursitis 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 bursitis 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 that may be helpful, as people with fibromyalgia and other pressure-sensitive conditions find themselves in a situation similar to yours (but it will also confirm that there isn’t a single “best” combination of materials that will work for everyone with fibromyalgia).
Latex and memory foam in the upper layers of the mattress tend to be two very good products at pressure point relief. Of course, they are part of a complete mattress system so they work in conjunction with the rest of the mattress componentry. And if you have a base mattress underneath that uses lower quality componentry (like your current Sealy mattress), this can negatively impact your overall comfort as time goes on and the lower-density foams lose their elasticity and comfort.
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.
If you do decide to select a latex topper, there’s some good information about selecting toppers post #2 here and the posts it links to. There’s also a list of some toppers that can be returned here. If you did use a latex topper on your current mattress, I would still recommend rotating the mattress and the topper, but you shouldn’t have to do so every night.
Zoning systems of various types can sometimes be useful and worth considering for people that have more difficulty finding a mattress with the right “balance” between comfort/pressure relief (under the shoulders especially) and support/alignment/pressure (under the hips/pelvis especially) or who have more challenging circumstances or sensitivities as yours, body types that are more difficult to “match” to a mattress, more complex medical issues, or who have a history of having more difficulty in finding a mattress that works well for them. There is more about zoning in this article and in post #11 here and the additional posts it links to but once again the only way to know whether any specific mattress (zoned or otherwise) will be a good “match” for you in terms of PPP will be based on your own careful testing and/or your own personal experience. Also look in post #2 here. Flobeds, a site member here, has quite a bit of experience with various zoning systems with their V-zone mattress that is configurable, and while you may not necessarily be looking to purchase one of their systems, the information they provide could be a good reference for you, as you have such a specific condition and you’ve gone through so many mattress combinations without much success.
Phoenix