First time side sleeping quilt user who plans to use a solo tarp?
Let's hope you ordered a wide (56-58") in the upper torso/shoulders and long length. Narrow quilts work fine for many users, but sidesleepers should go wide IMO.
I find I dont require a bivy paired with my tarp now having moved up to a wider variably tapered quilt. Below 20F the likelihood that I will pack a bivy along increases some but is still dependent on the weather, specifically moisture (*snow, driving rain).
Wide quilt and a large coverage tarp certainly facilitates easier temperature management for me, leaving the bivy as an "as needed" item in my closet. I find the generous coverage of a large tarp and the warmth and flexibility of a widely cut quilt are worth the additional oz., as well as simpler to use while out. Fiddling with a bivy, tarp, ground sheet, pads, and quilt straps became a bit fussy and I found myself scratching my head going "Why am I doing this?"