[16M] I’ve Got To Be F***ing Up!

I have nothing but a few blankets and a single pillow on the hard, matted floor of my room. I have dealt with back issues for a while and my posture has suffered, but I started this lifestyle believing a more natural, ancient habit could improve my health and overall well being. The first night was rough; I was so exhausted I almost slipped into sleep paralysis. I am not used to sleeping on the ground, so after about an hour I gave up, moved to my bed, and fell asleep immediately. Now it is the second night, and when I try to lie flat my back will not straighten against the floor without intense pain; it feels like someone is pulling my chest toward the ceiling with a chain attached to my shirt, my spine arches so only my hips and shoulder blades touch the ground, and there is heavy pressure in my lower back. Is the lack of cushioning causing this, do I at least need a yoga mat or something similar, or does my body just need time to adjust? I really want this to work, any advice would help.