Either Exped Synmat or Thermarest NeoAir. I’ve the Winterlite and my wife has the Hyperlite, used them to -16C in Arctic Finland.
Have a search on Bearbones forums, lots of similar questions.
Be careful with the Synmats – if you inflate them fully then the internal welds are under stress so if you kneel on them or drop onto them then they’ll unzip. Just inflate to max then let a little air out.
I did get asked a while ago just how well they packed. here’s a shot of them, a cheap Multimat inflatable on the left, orange Hyperlite, red Winterlite with a 500ml and 750ml water bottle for comparison. The mats weren’t tightly rolled but did have pretty much all the air expelled.