Hi ikshwaku,
Okay... time for some follow up. We ended up needing to save some money so we went with the Brooklyn Bedding medium firm bed in King Size
Congratulations on your new mattress!

You certainly made a good quality/value choice.
My problem is that I'm feeling tremendous shoulder soreness in the morning on the new bed from side sleeping. Enough that I am afraid I will damage one or both shoulders in no time if this keeps up. I'm sure it has to do with my sleep position, but this never happened in the memory foam (which I hated for heat) or even on the crappy spring mattress.
I‘m sorry you’re having some trouble with your shoulder adjusting to your new mattress. Unfortunately I can’t diagnose via an online forum the reasons that you might be experiencing this pain, but I can make some general comments about things that help ease shoulder pressure for side sleepers in the hope that they are useful to you.
As I can’t see how you sleep, I can’t comment upon your sleep position or know if you’re inward or outward rotating your arm and placing it in a position that is contributing to this pain. I would be surprised if sleeping upon a mattress using the point elastic latex materials that your mattress does would cause permanent damage, unless you had a specific health condition that is causing some fragility in this area, or your sleeping posture is such that it is exposing you to issues of extreme compression or extreme flexion (of course, I only play a doctor on the internet

) .
Your new mattress, having better support characteristics than your old memory foam mattress, could be bringing to the forefront some changes that need to be made in your sleeping posture. You could also have some learned alignment issues from your old mattress, which does take some time for your body to adjust, as you’ve only slept on your new mattress for three nights. This adjustment generally takes anywhere from three weeks to three months, what I term a “period of retrogression”.
I would first start with your pillow and make sure that it is the proper thickness to maintain as neutral an alignment as possible (as you were concerned about). As your old mattress let you sink in too deeply, it is possible that your new pillow isn’t thick enough to maintain this neutral alignment when you are on your side, and this can place additional stress upon your shoulder.
The next thing you may wish to do is work on not placing as much pressure directly upon your shoulder joint and work on abducting your shoulder complex forward a bit buy hugging a pillow in front of you while you sleep. If sleeping upon your right side, this will allow your right shoulder to “roll forward” a bit, and also allow a surface upon which you can place your left arm. Both of these things will assist with shoulder joint pressure issues.
Something else to consider is the placement of a pillow behind you which you may slightly lean up against, akin to taking a nap on a couch and leaning up against the back cushions. This allows you to again lean back a bit, rolling your shoulder joint forward a little and taking some of the direct stress off it.
These are three suggestions that you may wish to try out and see if they help alleviate your shoulder pressure and pain as you adjust to your new mattress. If after trying out your new mattress for a month or so you still find that it is uncomfortable for your shoulder, I would contact Brooklyn Bedding and see if they had any options for you. It could be that you desire the less resilient feel of memory foam and you may end up considering a memory foam topper for your mattress. Or it may be that this mattress isn’t agreeable for you, in which case you at least had the foresight to choose something that does have a good return policy. But you’ll definitely want to give this more time to test things out. I’ll be interested in seeing if any of my suggestions are assistive to you.
Phoenix