How about a trundle bed?
We got bunk beds last fall, and my girls (6 and 8 yrs) loved them although there was a lot of climbing and jumping and playing with the ceiling fan. I took off the ladder so my two year old son wouldn't climb up, but by the time he turned 3 he was able to climb up without the ladder (and get down). His sisters taught him how. We have had no accidents. The extra space in the room was great. But...
I took the bunks down and separated them into two twin beds for the following reasons:
-After the novelty wore off, the girls tended to sleep together in the bottom bunk.
-It was a major nuisance to try to make the bed or change the sheets.
My advice: get the beds that can be separate twin beds in case you don't like bunks. Or try a trundle bed. My 3 year old son has one that slides under his sister's bed during the day.