Tell me what your baby is sleeping on? We always slept in a diaper, un…

Tell me what your baby is sleeping on? We always slept in a diaper, underwear, socks and a thin cotton sheet. Now he seems to be used to sleep without a sheet, and in the evenings, tantrums begin. Specifically before bedtime. I think maybe because of his hands and feet ?‍♀️ or he doesn't want to sleep. We are three weeks old. In general, I don't know why the tantrums happen, as soon as we pick him up it ends. I thought about the tummy, but he can lie down calmly, just as long as we lift him.