M.,
Both of my boys have bunk beds - which means no box spring. They are fine. We bought better mattresses and for my oldest son, because he has the futon double bed/couch at the bottom of his, we bought the 8" mattress and then one of the memory foam pads. It's really comfy!
IKEA has some great platform beds! If the mattress is too hard for your son, get a memory foam pad to put over the mattress.
Many platform beds have storage underneath....which is great!!
Since I have two bunk beds - and a 14 and 12 year old who have had bunk beds since they were 3? Yes. I would invest in it!