I have to put out the word and thank everyone who participated in this forum with great ideas for a better nights sleep
We ended up buying two of the Thermarest ProLite self-inflatable (you can also blow into them to make them as firm as you like) mattress pads from REI. They are light weight made for hiking, great insulators, and gave us just the right amount of padding for a comfortable sleep in the penthouse. They are full size, but roll up into a tight small package for stowage. A bit pricey, but definitely worth it!
Who knows, we may even use them for penthouse wall insulation some day (if were desparate enough).