Hey everyone! 

I'm new to winter backpaking/camping. I’m planning to sleeping out in one of the bivouacs in the Alps. Specifically, I’m looking for recommendations for a good sleeping bag for winter conditions. I’ve been eyeing the Sea to Summit Spark -18, but I’m wondering if there’s a better option at a similar price point.(I’ll be carrying a lot of camera gear, so compactness and light weight are key factors)

I also looked at Therm-a-Rest sleeping bags, but they seem to be sold out everywhere. Anyone know why? They’re cheaper but seem to have similar specs to the Sea to Summit bags. 

Is the Sea to Summit Spark -18 a solid choice for a first winter sleeping bag? Additionally, I'll likely be sleeping on a wooden bench (not directly on the ground), so what r value should I be looking in the sleeping pad?

Anything else I should consider when selecting sleeping gear for this trip?

Thanks for the help!