Definitely a side sleeper, too. But also tend to roll all over the place in general, too. A specific bag recommendation would depend on your body measurements and type. I hands-down prefer a mummy bag over a rectangular, but have found that as I've gotten older I also prefer some extra room. I've found that bags labeled as "comfort-cut" mummy have done well for me personally - they have an extra couple of inches across the chest. I'm a male, 6'0, 190 lbs with a 44" chest (22" shoulder width). Bags with a shoulder girth (circumference) in the 64"-66" range seem to be most comfortable for me without adding uneeded extra weight. Generally, a bag labeled as a "performance-cut" mummy will be several inches narrower in the shoulder girth, and thus not provide much turning room inside the bag, unless you're pretty thin. My go-to bag for 3-season use here in AR is a Mtn Hardwear Lamina Z Spark. Narrow enough to save weight, but wide enough (65" shoulder girth) to accomodate my tossing-and-turning.
Other advice is to visit a local outdoor sporting goods store, kick off your shoes, and climb inside several different sizes/styles until you find one that feels good. Even if the bag that feels/fits the best isn't exactly what you want, write-down the 3 measurements from the tag (shoulder girth, hip girth, foot girth) and shop using those as a guide. Always allow a little extra room for extra layers when extending a 3-season bag into the shoulder seasons. Hope this helps.