Here's what I did and it worked well. I HIGHLY recommend that you do this (it would be even more important if you were pregnant, but since you aren't, you have plenty of time.)
Go shopping and pick one store where they have several things that you would be happy to have in your son's new room. Comforters, sheets, lamps, rug, etc. Take pictures of them with your cell phone if you need to so that you can remember them. Go home and tell him that since he wants to sleep in a bed, that now he is a big boy and he can have a big boy bed and room. Make a BIG DEAL of the fact that you are going to take him to the store and let him pick out his big boy room. Then take him and show him everything you have chosen and let him make the final choice of what he can have. If you want to show him the pictures on your cell phone first, that might help. Just don't include anything that you aren't willing to buy so that there are no arguments. (I chose all primary colors so that I wouldn't have to worry about color coordination. All the primary colors match, period.)
Do NOT let him in your bed, not even once. You will rue the day you did it if you allow it. And then you'll be on here asking how to get him out of your bed. That includes letting him lay down with you until he falls asleep. You cannot believe how he will punish you for that decision if you allow this.
It's easier that you want to change rooms rather than transform his current room. Don't get a toddler bed. Get a real single bed with a good mattress. We had a very old mattress which didn't bother my son one bit, but when I got pregnant, I'd slide off of it when I sat down on it, and it was quite awful. A new mattress solved that problem - thank goodness I didn't end up on the floor before we bought a new one...
Put together the new room after you buy everything. Make it a fun project. Spend time in there with toys and books, and put his clothes in the room LAST. Let him help you with the entire process. Make sure the sheets are washed and softened so that they are comfortable. Make sure you get a SMALL pillow - not an adult size. It needs to be rather flat - not fluffy.
You can ask him if he wants to sleep in his new bed after you have everything ready. I would not push it. He may end up waking up in the middle of the night crying if you go too fast in the process. Let him take the lead and don't push him.
Most importantly, don't wait for him to fall asleep - tell him goodnight and walk out, close the door, and walk away. He needs to know this from the get-go. If he comes out in the middle of the night (he can actually get up and leave the bed now that he's not in the crib), don't engage with him AT ALL. Lead him back to his bed and then walk out again and close the door. Over and over if you need to. NEVER sit in there with him so that he can fall asleep, or he will wake up every night just so that you will sit with him.
The reason you don't want a toddler bed is that he will grow out of it soon and you'll just have to buy yet another bed and more bedding. Too expensive!! However, you can buy a bedrail at Toys R Us so that he won't fall out of the bed. Put it up just before you walk out of the room for him to go to sleep. And then put it down when he wakes in the morning and leave it down.
Leave the crib in the other room for a while until he is no longer paying any attention to that room. (I left my crib up because I was pregnant. By the time the baby came, my son no longer cared that it was his old crib and wasn't jealous of the baby sleeping in it.)
Good luck!
Dawn