I get a sore back most nights. I use the My Breast Friend pillow. I love it except for the part in the back, which during marathon nursing sessions makes my back worse. I try to always have extra pillows propped behind me. I also try to lounge back, if possible.
Make sure your bringing baby to you and not hunching over to bring your boob to baby. I find regular pillows help more than a boppy or nursing pillow, I also find sitting Indian style helps.
Re: Sore back and neck?
Try side line nursing. It's saved me especially at night.
If that doesn't work then make sure your back is as straight as possible, put LO on a pillow to raise up, and roll your shoulders back while holding.