Re electric blankets, we always had one on top of Larry in his wheelchair in the living rm but of course we were monitoring it. It was low voltage but he always needed it at the highest setting. Our LR has a lot of windows.
At night, Mike's caution is warranted so we used a low voltage mattress pad that went between the mattress and a regular mattress pad. On top of that was his foam overlay, a waterproof mattress protector, the slip sheet we used for getting him up and the fitted sheet. With that, Larry's settings were usually 2-4. You might not think the heat could get through all those layers, but it does.
The key to both of these for safety is "low voltage." And if there is a short, the blanket or pad will not turn on.
We didn't have a Trilogy -- I hate Respironics machines -- but if condensation is an issue at night for Darcy, why not go back to the S9 for sleep? In any event, I would never have a machine at night that wasn't using heated humidification, preferably w/ temp and humidity set separately as you can do w/ the S9s and ClimateLine tubing. For those who have tried and thought the air was too hot or wet, I'll bet you only had one setting, not two.