Sorry to hear about your son. Broken collar bones suck. I broke mine when I was about 10 and can still remember having to wear that brace and sleep on my back for 5 weeks.
With the remodeling I've done only the Single Queen drop down remains and I use that but it rests about 5' off the floor. (Mine is a front kitchen and I removed the bench seat.) But nothing wakes me up faster then swinging over the edge and sliding downwards and finding that I've missed the ladder entirely! I've made a point of centering it on the bed (only about 30" of center aisle is available) and usually look up to align myself on the vent before swinging over but sometimes I forget. I've fallen three times doing this but its only a matter of time before I break something.
Of course I've got this other fear of rolling off the bunk while sleeping. What are others using as guard rails (for adults?)
not sure what adults are using, but i "tested" the one above and it kept me in place. it also leaves enough room to get in at either end so getting in and out is not a prob either. buy it and give it a try, they have a good return policy so you wont be out much, if anything.
I hope your son has a speedy recovery. My son sleeps on the bottom bunk and since we have 3 gear bags I line them up along the bed and it's worked so far. Plan "B" would be a tie down