I'd be reluctant to sleep on a different floor to ds because I'd worry about fire.
We have a townhouse with bedrooms on the top floor - you really can't hear anything on the ground floor where the kitchen is so we still use a baby monitor while we are downstairs. I guess if our bedrooms were on different floors I'd keep it on all night.
If we did move into a house with that set-up, think I'd get the local fire safety people out (they will visit any house for free to do a home safety check) and follow their advice.
Perhaps I'm particularly concerned about fire because when I was a kid, we were driving home when we saw loads of smoke that looked like a house on fire. The closer we got to our house, the more obvious it was that it was our neighbourhood, our road, our end of the road... the dawning realisation is a very strong memory.
Fortunately it was our garage and the next door neighbour's, not the house (turned out their teenage daughter had been smoking there). But that feeling in the pit of your stomach was horrid.
Another time, our toaster burst into flames and the damp cloth trick I'd seen on Blue Peter didn't work. We fetched a neighbour who put it out (think mother had gone to work but au pair had sneaked out - she was sacked).