Hi gp193,
Once again it seems you’ve been doing some good research and already identified some of the variables that could be involved in the firmness of your mattress 
[quote]I am going to give the bed at least a week before I make any adjustments, as there are a few variables affecting the feel of it. Right now, I feel that the bed is too hard for me to sleep comfortably on my side. While it’s supportive on my back and my lower back pain is better, it is uncomfortable on my shoulders and hips when I roll onto my side. Here are some things that I think might be making the bed feel so hard compared to what we tested in the store.
- It’s brand new. Supposedly it will get a bit softer as we break it in, after about a week.
- Mattress protector: we are using a thin, membrane-type protector since we need to protect the bed from liquid (toddler is often in bed with us). I wonder if the protector is causing a more solid feel to the surface of the mattress.
- Sheets: we are using regular cotton sheets and I suspect a stretchy jersey sheet might feel better.[/quote]
All of these and a few others (including your pillow) can certainly make a difference with shoulder and upper body firmness issues (see post #2 here). The break in period and adjusting to a new mattress can take up to about 90 days or so but in most cases less than 30 is more the norm.
If your protector is fairly tight and creating a “drum like” effect then it can certainly affect how easily you sink into the top layers of the mattress. The sheets can do the same although this is less likely.
Overall the first step is time and then if you need to make further fine tuning adjustments then the good news is that this is possible.
When you have a mattress that works well for alignment on your back but creates pressure issues on your side and you have eliminated other options … then the “best” approach is to look at the top few inches of the mattress (in the range of 3" - 5" depending on body type and sleeping positions) and then make changes that can soften up these top layers “just enough” to allow your shoulders to sink in a little more. Depending on the specifics of your mattress … this could involve a slightly softer top layer, a slightly thicker top layer (adding a topper) or a softer innerspring all of which can affect the performance of the top few inches of the mattress and how well it “allows” your shoulders to sink in just a little more without significantly affecting the deeper firmness under the pelvis.
If a topper or a mattress pad is not too thick … it can affect the surface feel but still won’t be thick enough to “disguise” the feel or performance of the latex. If you use a fiberbed type of topper (such as a wool topper or a polyester fiberbed) … it can “feel” cushy on top but it may also affect the ability of the latex to contour to your body so it may not “allow” your shoulders to sink in more but it can help with “point specific” pressure relief. This would be a 'feel" based form of softness more than a “pressure relief” form of softness (you can read more about the different types of softness in post #15 here).
The key with most changes is “just enough” but no more so that the balance between pressure relief and alignment/support is maintained.
Phoenix