Bedding don’ts

Say one thing about sleep say my body is five kinds of finicky. It takes into account not just everyday mundane like the weather and time but also the mattress.
Yes, I cannot get sleep if the bed or its mattress in question is even a little bit disagreeable.
The kind of mattresses that I want/need are the firm kinds which absorb your body without letting it sink in like the softer version of mimsy mattresses.
On the opposite side of the spectrum are mattresses which make you feel like you're lying on top of it, the feeling of being not one with the bed is so real that sleep doesn't come and it's always a struggle for me to find the perfect blend of firmness and comfort which is why I do a bit of DIY and line the bed with bamboo mats and thin layers of thick foams etc, which is a story for another day.
Right, so the bed here has been custom prepared to my liking and I did enjoy good sleep except the past couple days when the right side of my neck and shoulder developed a strain which I know to be a symptom of bad sleeping posture that usually only happens on beds I dislike.
Most odd, this shouldn't have happened, because the last time I got this crick was ages ago in a hotel room.
A bit of inspection revealed that that bedding under the sheets has been changed a bit in my absence, undoubtedly with good reasons to augment my comfort because I'm not a good sleeper unless I supplement myself with a particular botanical medication which is quite out of question here and I needn't talk about my age old rancor with nighttime snooze; on finding the change and knowing the cause of my odd neck/shoulder crick I was visibly riled because the pain is severe and has increased in the past couple days; this ache not to be confused with another shoulder neck pain that happened due to muscle injury while working out.
This strain in question is similar to one that happens during bad sleeping posture but not exactly and to me the root cause was staring me in the face.
Now I shall make a switch and put back things as they were under my sheets or I shall have to change beds or even switch rooms.
Yes it's that serious.
I can't sleep on a mattress not to my liking.
Gah!