From a fellow side sleeper I am not a fan of the true mummy style sleeping bag. It generally does not have enough room for me to curl my legs.  Also, I wouldn't recommend shifting on your side taking your whole bag with you as a lot of bags have the insulation mapped to areas of the body that generally need more insulation (ex: more insulation in the feet for women). 

One of my favorite bags to recommend for side sleepers are the NEMO sleeping bags.  They're a roomier mummy style that allows for better curling.  Also a lot of the bags have ventilation slits that you can unzip to allow heat to escape without having to open the whole bag and let cold air in.

Happy Adventuring!

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