My sister and I sleep in just one small bed so I am used to sleep in fetus position. Our mother had thought before of buying us a bunk bed so we can sleep comfortably and to prevent from hitting each other while asleep but it didn’t materialized due to financial constraints.
Anyway my older cousin had three kids already and two of them are boys I think they could make use twin over full bunk beds for boys for their room so they could sleep comfortably and without a problem. You know how little kids sometimes especially boys. Bunk beds is not that dangerous as other mother thought to be, most of the bunk beds has secure border so even if the child move a lot when asleep he won’t fall from the bed, it has also a stair for easy access to the top of the bed.