We are co-sleepers as well. It was around 2 years that we started the process of putting our son to sleep in his own bed. However, to start with, we let him fall asleep in our room and then moved him to his "big boy" bed. We had night lights so that he could find his way back to our bed when needed. When his brother came along, he had just turned 3. Part of our big push for getting him into his own bed was issues with my back during the pregnancy and also knowing that the third was going to be a third c-section. I didn't want him to hit my incision when I came home.
Other suggestions we have read and seen are to put a mattress (either crib or regular single mattress) on the floor in your bedroom. Put the two year old to sleep on the mattress, right next to your bed. After a couple of weeks move the mattress a little further away from your bed. My son would lie in bed with us to go to sleep until he was about 3 1/2. Then my husband took the initiative and started a new bedtime routine in his big boy bed (which he had been sleeping in for some time without issue. It was just he fell asleep in our bed and my husband moved him.) Now he is 4 and goes to sleep in his own room without issue 70% of the time. He still tells me at times that he just wants me. It breaks my heart but I stand by his Dad and tell him to give me one more hug and kiss and go up to his own bed and I will check on him in a little bit.
Our oldest and only daughter is now 9. She also was a co-sleeper at first. Then she like her brother would go to sleep in my bed with me and her Dad would move her. She decided on her own at about 3 1/2 that she just wanted to go to sleep in her own bed. She sleeps with a radio on in her room. It helps to drown out other noises in the house and takes the place of her dad snoring. ;)
In the immediate time, though, one thing that helped after my youngest son was born, is a Snooglie pillow. It is a pregnancy pillow that is shaped like a big C. I would put the C facing me and the newborn and I would be on one side of the pillow and my older son was on the other. It acted as a little bit of a safety barrier between the my son flailing and rolling in his sleep and his newborn brother.
Another alternative is a pack'n'play in your bedroom for the newborn until he is a little older. You can set it up right beside your bed so that you can sit up and reach him (they also have some that are co-sleeper ones that somehow attach to your bed). This would allow the baby to be near you so that you can reach and fill the needs of your newborn while still having your son right there as well and free you from worrying about the two year old rolling on or kicking the newborn in his sleep.
Anyhow, these are just a few suggestions. I hope that they help. I know there is no "easy" solution. You want to snuggle both kids but you want them to both be safe as well. So I wish you luck as you figure out what works for you. One final suggestion is to check out Dr. Sears online or his Baby Book. I believe he is an advocate of co-sleeping (although it is late so I could be mistaking him for one of the other doctors but I don't thinks so. I believe it is a part of attachment parenting which I know he advocates).