Yes it's healthier to sleep on the floor and most people actually get much better sleep when they sleep on the floor instead of on a mattress.
I sleep on a mattress most times.
However sometimes I'll be laying on the floor with my 3 year old son and watching TV with him during the night and sometimes we fall asleep on the floor.
I find that I sometimes get much better sleep when sleeping on the floor instead of on my mattress.
There are some cultures that still sleep on the floor and a lot of people slept on floors for thousands of years before the mattress was invented.
So yes it's healthy to sleep on the floor and sometimes you get better sleep sleeping on the firm floor versus sleeping on a softer mattress.