I would like to go on a short backpacking trip over thanksgiving weekend in Utah, Nightly lows where I would like to go are in the 3℉ to 10℉ range.

I currently have the following sleep system
- Nemo Disco 15 (17℉ comfort, 4℉ Limit)
- Big Agnes Campmeister Deluxe pad (R value of 7)
- Patagonia Fitz-Roy 30 (30℉)

With this Kit I have 3 options

1. Ideally I would like to put the 30℉ bag inside the 15℉ bag to get down to lower temps. I have heard that stacking sleeping bags is not recommended because of reduced loft, the Nemo Disco is a very roomy bag so I think this could work
2. Buy a 25℉ Quilt and put it on top of the 15℉ bag. I have heard that a quilt on top of a bag will work.
3. buy a zero degree bag or quilt. I would prefer not buying a new quilt, especially if it is a 0 degree. I would rather buy my first quilt that I can use for more parts of the year

I would love to hear anyone's opinions.