from shulchan aruch orach chaim 2 mishna brura there
(davka feldheim translation
2: THE LAW REGARDING PUTTING ON CLOTHES mishna berura 1. "...For this reason, one must likewise take care always, when not compelled /to do otherwise/, to avoid exposing even a little of any of his flesh which is normally kept covered by clothing all the time..." 2. "I.e., when he gets up and emerges from underneath the covering of his sheet, where he was lying naked after having removed his undershirt..."
239: THE LAW WITH RESPECT TO /THE READING OF/ KERIAS SHEMA BEFORE /GOING TO/ BED 2 When one takes off his undershirt, he should not turn it around /at the bottom and lift it/ upwards from below, since if /he does/ so his body will become naked. Instead, he should slide it off over his head, /after/ having covered himself underneath /the undershirt/ with his bedclothes /beforehand/, and /thus/ get into bed.)
it seems that what is normally kept covered by clothing should not be unclothed unless no choice and that a sheet is considered covered (clothed)
if i want to change my clothing during the day
can i use a bathroom as a covering wile i change my clothing? or do i need to go under a sheet?
PS i understand about AYLOR but i am looking for sources