jet, Phoenix really understands the physics of this, so I copied what I think is an important paragraph from one of his posts:
“The type of issues you are having can be because of comfort layers that are too firm but with your higher weight it is equally likely (perhaps even more likely) that it could be because your hips are flexing beyond their neutral range and firmer support layers may be helpful to prevent your hips from overextending. Your experience on the Corita and on softer layers may be pointing to this as well. This firmer support can be accomplished by some layer rearranging (with each one being tested for at least a week) and would give you the opportunity to find out how your symptoms change (regardless of whether they are completely resolved) with different combinations of the balance between pressure relief and support.”
I believe he is saying that your hips may be sinking in too much when you are on your side and that perhaps you should swap the firm and extra firm so that the support layer gives you more support. Personally, I found my latex mattress surface softened significantly so I would be inclined to keep the medium on top for at least a week. If you have a digital camera you can try taking a picture of yourself from behind while lying on your side. My suggestion is to take the picture after you have been lying on your side for a while, so you settle in. Phoenix could make a better guess as to whether or not you are sinking in too much.
Check this thread to see what I am talking about:
https://forum.mattressunderground.com/t/new-mattress-is-it-too-soft
I have one other thought. I used to be primarily and stomach and side sleeper. About ten years ago I was diagnosed with sleep apnea and starting using a CPAP machine to sleep. Because it required wearing a mask I had to learn to sleep on my back for at least part of the night. Sometimes I still take the mask off and spend some time on my stomach. Have you tried moving to your back when your hips get sore?
Best to ya, Lew