Carpet definitely. Search out thread "What do you put on the floor" (My approach at post #41) On my third Jayco with light coloured carpet. It's always my first mod. Absolutely no regrets. Great heat insulation (summer & winter), sound insulation, and underfoot comfort. A search for "bunk curtains" will also give you so great ideas.
It was your thread that made me suggest it to my husband originally! I don't know if he liked the idea at first but after the freezing feet last night I'm pretty sure he is sold now.
Will definitely be pinching some ideas from here for the curtains, saw a couple of easy looking ideas not long ago.