Have you considered a quilt instead of a bag? I've just ordered a DIY synthetic quilt kit myself (around $100 for a 40*F-rated one). The insulation of the bag under you doesn't insulate as well since it's compressed anyway, so just eliminate the bottom of the bag. This saves packed space and weight. Make sure you're going with the latest synthetic fill. Climashield XP seems to be the latest and greatest.

If quilts sound too radical, Big Agnes bags just have a pocket for a pad on the bottom.

It sounds like your style of camping might be well-suited for a hammock?
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Bushcraft Science: It's not about surviving in the wilderness, it's about thriving in the wilderness.