You can just put the baby in a bassinet during that time, and by the time your baby outgrows the bassinet, your son will be about old enough for a toddler bed. They say that 15 months is actually the age, but I never would have done that with my son. I am a single mom, living with my dad, sharing a room with my 2 1/2 yr old. When he was little, I had a bassinet next to my bed. He ended up in my bed most the time anyway cause it was easiest to nurse him that way. When he started to crawl, I set up a pack-n-play for him to sleep in (I don't have room for a crib, and felt bad having my baby sleep in that, but it was the only choice), and he did fine in it. He eventually ended up back in my bed, and by 2 could easily climb out of a pack-n-play anyway, so it really didn't matter where he was. Now, since I have a queen bed to myself and no room for another one for him, he just sleeps with me. I will move him into his own bed when I am able to move and give him his own room, but for now, thats the way we have to do it, and it works fine for us! They will be fine. Most people I know with toddlers, the toddler climbs out of the bed and sleeps on the floor for a while anyway, and that won't hurt them either. As long as the bedroom is safe, he will be fine wherever you put him. Good luck with your new baby! :)
J.