I see a lot of recommendations for sleeping pads for side sleepers (after reading reviews, I'm most likely going to go with the Big Agnes Insulated Air Core Ultra), but what are your recommendations for sleeping bags? Are mummy bags really that uncomfortable for side sleepers? I'm currently looking at the Big Agnes Katherine SL 20. 

I'm also wondering if people sleep on their sides inside the bag, or if they shift on their sides taking the whole bag with them. 

As you can probably tell I've never slept in a sleeping bag before.