Trying to change a 1 1/2 year old's behavior while you have a 2 week old at home seems impossible to me. Poor little guy! Think of it from your son's perpective -- he didn't ask to have a sister or brother! Now, he's got one, AND he/she's getting ALL the attention HE used to have (so cute!! aww!! she burped!! blah blah), AND he's not the baby anymore! NOW HE's getting kicked out of HIS bed (it's really yours, but to a toddler, everything's MINE)??? What's next? Is THE BABY going to sleep in the bed with you now??? "What in the world???" is what your toddler must be thinking! Mommy went away for while, and then came back with a new baby. Don't know where the kid came from but I got here first! I'm not changing a thing!
Think again about what you are trying to accomplish here. I say, make it easy on yourself and your kid. You're still postpartum! You don't deserve this stress. How about getting a co-sleeper or bassinet for the baby, put it next to your bed, and doing all your tasks for baby while in your room with your son is still co-sleeping as before (change baby on the bed, feed in chair in the room, etc)? Even if your son wakes from the commotion, he likely will take this better than being left alone right now. You may want to take this approach for a few weeks, until newborn's older and 1 year old is more used to the baby being around. Then, consider transition to floor using a sleeping bag or toddler/kid air mattress, even maybe using his crib mattress on the floor, and keep in the room but separate from the big bed, if that is what you want to do. When he is 2, he may be able to better accept the idea of sleeping alone.