The humidity here doesn't seem to bother my knees, but the cold, damp does.
Fortunately, we only have those conditions here occasionally.
You figure out ways to deal with that.
We have been here since early 2011. We both feel an appreciable difference in our joints, but it has been gradual.
We too, left a home with multi-levels. That has helped a lot.
For us, sensible exercise on a regular basis, rest when appropriate, floors that don't kill your body to live on along with reasonably healthy eating are all things we can do with ease here.
We consider that the focus is now on nurturing ourselves. The hustle bustle grind of our previous years is done now... we have graduated to enjoyment.
That mindset alone ( which took awhile to sink into our heads) makes you FEEL GOOD ALL OVER.