Positions during pregnancy?

I don't normally like to talk about my sex life, but I hope I can get some useful advice here. I'm 21 weeks and my belly is starting to make our normal positions difficult. My husband also has a bad back so when he has to hold himself up for awhile in certain ways it starts to hurt him and other positions (like doggy style) have always been very uncomfortable for me. He's also been getting scared he's going to hurt me or the baby on top of me or if I start to have a hard time catching my breath.

Has anyone else dealt with this or any advice on ways or positions to help?