bag plus liner

[weasel and bunny]

I am looking for an upgrade to my heavier synthetic bag and found a possible solution.
Lafums Warm N Light 800. 1lb 12 oz. rated to 30 degrees
I am looking for something for a March 15ish NOBO. I want a 20 degree rating, so a liner would be required with this bag to get me there.
My questions are; has anyone had experiance with this bag or type of setup?
Any recomendations for a light down bag for a 20 degree rating?
Can I go lighter than 1:12 with an additional liner without a budget buster?

[butts0989]

here's my set up: Western Mountaineering Summerlite (19oz) and a Sea to Summit Silk liner (4.8oz). I sleep pretty hot so ive taken it down in the teens wearing some of my other clothing (Montbell down jacket, rain pants). its super light but costs a bit of money.