Those are the best.
I have slept on my side for about 1/2 my life and still do from time to time. Back sleeping seems to be optimal to me.
If you are losing breath while on back you might be suffering from obstructive sleep apnea. Shallow breathing and probably a snorer maybe acid reflux?
Its not stone I am not that hard-core lol still has plenty of support. Sounds to me like you have some health issues that don't allow you to properly sleep on your back because healthy people should have no problem sleeping on either side as they have done for hundreds of thousands of years. Soft beds are relatively recent thing or were exclusively available to the ultra wealthy like royals and aristocracy while 99.9% slept on hard beds.
thinking it might be apnea related. reflux, possibly. i dont usually snore
sub optimal genetics in the sleeping category
my bed journey been a tortured one. i had a very firm queen bed, which was too firm so added a 2 inch latex topper on it. that worked well for a while. topper felt like a crutch
frankly i prob overspent. i probably could have shopped more and spent half, but bed shopping has been pretty time consuming.
pulled the trigger on one that seems to fit the bill, pretty firm yet has some give for shoulders/hips. with a decent sleep trial. ive done sleep trials on highly rated beds, that i ended up ultimately returning (too soft as you mentioned)
so if this bed rig pans out then great. expensive but atleast ill use it every day. not much i splurge on, this was an exception
next time i will factor in a trip to japan during my bed search