Hi gp193,
If the comfort layer works well on the firmer side and not on the softer side it’s much morel likely that your hip pain is not so much from the firmness or thickness of the comfort layer but from the amount you are sinking in on the softer side. It may be that your hip joint isn’t in neutral alignment on the soft side and this is causing some strain on the joint (muscles and ligaments) which may be the cause of your discomfort rather than actual pressure. If you were feeling the discomfort on the firmer side then it would be more likely to be a pressure issue which could be related to the firmness or thickness of the comfort layer.
Most mattress protectors will have some effect on the ability of the foam layers underneath them to contour to your body shape as well as affecting sleeping temperature in some cases. It may be worth considering a stretch knit cotton protector which is very stretchy (like a jersey sheet) and may have less effect than one of the semi breathable protectors and also allow more airflow which would be cooler than the semi breathable membrane protector. Of course the down side is that it only absorbs moisture and isn’t water resistant or waterproof. There is more about the pros and cons of different mattress protectors and some links to some sources in post #89 here.
Based on your experience it seems like changing both sides to the firmer core may be a better solution (since it seems to work well for you). A padded mattress pad may reduce the ability of the latex below it to contour to your body even more and make it a little firmer.
If you were experiencing pressure points then this could be a good option but again it seems like the thickness / firmness of the comfort layers don’t seem to be the issue if the firmer side of your mattress is working well for you.
Phoenix