Sorry to hear you had a bad night. I've a couple of thoughts, though not a definite answer!
I think cold damp air does feel a lot colder than cold dry air, so when siting your camp its worth trying to avoid localised areas of high humidity as much as possible. The still clear conditions you describe will allow cold damp air to pool in valleys, especially beside rivers, and while these appear attractive places to camp, in practice you might well be significantly warmer on a knoll raised above the valley floor - I don't know if that might have been an issue?
You're clearly trying to learn from your experiences, as do I. To that end I've recently bought a small "fridge thermometer" - only about a fiver and minimal weight, but provides interesting information on how cold it actually got overnight. I'm hoping this will allow a more informed idea of the limits of my sleeping setup, rather than just assuming that the temperature I experienced was the forecast minimum for the area.
When it does get colder than expected, a hot water bottle can make a big difference. Make sure whatever you're using as a water bottle can take boiling water (metal bottles are obviously fine, but so, I've found, are plastic coke bottles!), fill it up and take it into bed with you. Makes a substantial difference for quite a while.
Finally, I'm another fan of the silver backed insulation under the neoair. Inflatable mattresses are quite good insulators, but insulation effectiveness is to a considerable degree dependent on thickness. So where your hip is pressing into the mattress for comfort, there might only be a few mm between you and the ground, and I notice the cold coming through in such spots in a way that I don't with an extra thin layer of reflective insulation underneath.
