Hi Sekhmet,
Thanks for the update … I appreciate it 
While I would normally suggest giving a new mattress at least two weeks before making any changes … if your husband isn’t sleeping well then I can certainly understand that he may want to make some “fine tuning” changes a little bit sooner … especially if there isn’t any signs of his experience changing or improving over time.
I’m not sure of the reasons for his discomfort or the actual “symptoms” he is experiencing but there is some good information about the most common symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here.
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”.
These posts are the “tools” that can help with the analysis, detective work, or trial and error that may be necessary to help you learn your body’s language and “translate” what your body is trying to tell you so you can make the types of changes that have the best chance of reducing or eliminating any “symptoms” you are experiencing.
If he thinks that the mattress is too firm and wants to try a softer comfort layer to provide some additional pressure relief then it would make sense to try your side for a few days (although I would encourage him to try and wait a few days longer just to see if there are any changes in his sleeping experience that he can identify). In this case I would also make sure that he tries your side for more than just one night so that he can identify more of a pattern in how it feels or how his experience changes compared to his side and make sure that any change in his experience isn’t just an anomaly. If his side is too firm then there are also some suggestions in post #2 here that may be helpful as well.
If the mattress is too soft (which will most often produce lower back “symptoms”) then it would make sense to exchange the middle medium layer with the bottom firm layer to provide some firmer support which may improve any alignment issues he may be experiencing.
The “best” suggestion of all though would be a more detailed conversation with SleepEZ so you can take advantage of their knowledge and experience over many years with other customers that are in similar circumstances and have experienced similar “symptoms” so that they can provide you with some guidance and insights about the type of changes that would have the best chance of success.
While I realize that it’s not always possible to wait as long as would otherwise be “ideal” … I would make changes as slowly and incrementally as possible so that his body has the chance to adjust to each change for a few nights rather than making changes too quickly or assessing the results of any changes based on only a single night’s experience.
Phoenix