When I hear the "S" word I immediately think car camping and not serious backpacking. I have three for my family including a 0 degree model. The loft is adequate but I would not actually use it near 0 degrees because it lacks a draft collar. I think Slumberjack's temp ratings are way too optimistic. But if you don't mind the bulk and you're not going very far they may be for you.

If the dog is going to be IN the bag with you I would avoid a mummy.

I'll repeat what I wrote in an old post: When it comes to sleeping bags you can have light, warm, or cheap.

Pick any two. You can't have all three.