Search:

Keep your current Bivvy, get a lightweight groundsheet to protect your inflatable mattress, and a fly. If it pisses down, and you've got JUST your Bivvy for shelter, you're going to hate being stuck...

birch: Definitely NOT directly on the ground. They insulate against radiative heat loss pretty well, thanks to their reflective inner surface, but will do nothing to protect against conductive heat...

32x26cm compressed and 2.4kg is not what I would consider compact, or lightweight.

There's one on trademe for $50 - better than any local price, or Amazon (once you factor in shipping). https://trademe.co.nz/1009836917

https://uploads.tapatalk-cdn.com/20160104/592ae75215bd7f1d45f302e2ae84eaab.jpg

Slightly bigger than a pump bottle. Website says 8.5oz (241g). No idea on subjective "warmness" sorry. Warm enough...

The SOL Escape Bivvy is a different material to their smallest, lightest bivvy bag, the Emergency Bivvy http://www.adventuremedicalkits.com/survival.html?cat=39

The Emergency Bivvy is a...

Lightest, most compact solution I'm comfortable using in relatively warm upper north island conditions is merino long sleeve thermals and long johns (which I carry anyway) inside a SOL Escape Bivvy....