It sounds like he may have his days and nights confused. Encouraging him to stay awake more during the day, specifically before bed, can help. Also, swaddling helps give a secure feeling. Keep the room dark and quiet at night.
Few people realize that having the baby in their room can actually disturb the baby's sleep. He can smell your milk, he hears you breathe, talk, roll over, etc.
My son had a womb sounds bear that played rhythmic heartbeat and wooshing sounds that he found very soothing. If he startled or woke out of pattern, turning the womb sounds on would soothe him right back to sleep.
As for co-sleeping, I'm not a fan. When I was pregnant I thought I would be, however, once my son was born I felt different. I couldn't sleep with him in our bed. I was afraid of rolling on him, putting a blanket or pillow over his face or even dropping him out of the bed onto the floor. In fact, I didn't feel comfortable sharing a bed with him at all until recently, and he's 2 1/2 yrs old now.