I like this topic! I've been sleeping nude for quite a while now. I'm in my 50's and still get morning wood. After a bit of getting used to sleeping naked, it no longer fases or turns me on.
When I was a kid, I wore PJ's once I hit puberty, the open gap fly was annoying and my hard dick would keep poking out. So I switched to my briefs, at first it was very stimulatiing, sexually, but after a while I got used to it. That's pretty much the way I slept until after college.
Once I switched from briefs to boxers in my late 20's, I started sleeping nude. I always leave my boxers over the bedroom door knob in case there's an emergency during the night or something.
Like others, I usually wear some gym shorts or boxers to bed if I'm staying with someone at a hotel or if a guest is spending the nite in my room..