We had 3 in a two bedroom! haha, but only for about a year after number 3 was born. I knew I'd be co-sleeping with baby and we had enough room in our room for a crib and swing so it worked out great. My daughter and son slept in the same room on a bunk bed. Bunk beds are great space savers, I was really interested in the full bottom twin top but there wasn't enough room in the bedroom so we did the twin/twin bunk. Even now in our new house, we kept the bunk beds set up in my daughters room and my son
always goes in there to sleep on the bottom bunk. The PP was right, kids feel safer sharing rooms and sleeping in the same room together.
The two that share the bunk bed now are 8 and 4 but we got the bunk bed when DD was 6 and DS was 2. No one's EVER fallen off, or even come close. Just make sure it has the safety railing across the top, (if you do the bunk bed route). I am one of 4 girls so we grew up sharing rooms, there was no other options. My mom put the two older girls together and me and my lil sis together. Throughout the years we'd switch it around and I'd share with my older sis for awhile, just to keep things fun but always went back to the original routine. I LOVED sharing a room, can't imagine ever not having one of my sisters in the room growing up.....I still miss the late night talks me and sis would have. : )
Good luck, but don't keep yourself from having another for that reason, everything will work out great!