Tempo

Look up spoon shaped bags. I have a nemo tempo 20 (which is synthetic) but they have down versions for more money. As a side sleeper it allows enough room to turn over in while also still packing to a compact-ish size.

I get the weight concern, but honestly for Washington trips, the Tempo 20's extra warmth is worth a few ounces if you're a cold sleeper. I used a heavy synthetic in the Olympics for years and never regretted it when temps dipped.

I'm from Washington as well and have the Nemo tempo 20 unfortunately haven't gotten to use it there. I've seen all the good reviews but I don't know if i'd reccomend it, it is quite bulky for backpacking and I've been a bit chilly in some temps that it claims to be good for. That being said I do like the bag itself and will still be taking it on my upcoming norway trip.

Really depends where you are, not sure where OP is exactly. Here it can be almost 30°C (86°F) during the day, but drop to around 0°C (32°F) overnight. I use a Nemo Tempo 20 and still need a warm liner sometimes. 

I haven't used these specific bags, but I did have a women's Marmot Trestles bag, rated for 15°F and I always slept very cold, even when temps were just hovering around freezing but not below. I bought a Nemo Tempo, rated for 19°F, and sleep significantly better, even when temps go below freezing. I also love the flap at the top, if it's cold or the sun is coming up and too bright, I pull it over my face and it's nice and cozy. The Marmot definitely feels like good quality, the zipper was really solid, it had a pocket (my Nemo Tempo doesn't), and just felt really nice, but did not keep me warm for some reason. 

I love my Nemo Tempo.  A quilt would probably be better, but they aren't in my budget. 

The forte is my favorite sleeping bag I’ve ever owned. Lots of nice details. Pillow holder, draft stopper, vent sections, phone/light pocket. And the spoon shape makes it so comfortable. I’m sure the tempo has a lot of the same, but the extra weight for 1 degree is definitely not worth it.