During the freezing state of my frozen shoulder nights were the worst. If my shoulder was rotated in the slightest or there was any pressure on it my whole arm throbbed. What I found worked the best was pillows propped behind my back while I lay on my side with bad shoulder up. The key however was using one of those bean bag travel cervical pillows. I would hook it over my waist and then rest my bad arm on top. This extended the shoulder a little bit, the same as it would be while standing, and held the arm in place as your forearm settled into the beanbag form.