Bugger, I have read this too late!
I have a POE ether elite, which is similar to the POE mat above, but is much lighter at only 400 grammes. So it is very similar to Kate's Neo Air, but much cheaper (I searched the net and got it for £45).
I too am a side sleeper, and find it ultra comfy. I have been in some very cold places recently (well I thought so lol), and so have used the ether elite with a thin cheap foam mat from my local camping shop (150 grammes and only £5). I have tied some very thin elastic across the foam mat at the top and bottom, so can place it on top of the ether elite for extra warmth. The elastic stops the mat sliding off no matter how much I wriggle...Which is quite a lot. The foam mat also has the advantage of making the sleeping surface wider by a few cm's so that is good too.
Overall I am very pleased with this combo as feel it is still very light (565 grammes), but much warmer than any of the self inflating mats I have tried