We used a tiny blow-up baby pool next to our bed to create what my daughter called "a nest" She would put her blankets and pillows into it and go to sleep. We eventually moved the nest into her room, and she transitioned nicely at around 3 1/2 into her bed. She is 4 now and even at at our new house without the pool, if she wants to come into our room, she brings her stuff with her and makes a nest! The pool slid right under our bed during the day and didn't cramp our style or our marriage since we are both into investing the time in our little ones when they need us.
Western culture is the only society that insists that children act independent long before they are ready. Our grandmas's advice of "letting them cry it out" or "training them to sleep in their own bed" is antiquated advice that we now know leads to DEpendenet and clingy behaviors in children, not the confident, INdependent ones we want to foster. Kids need their parents and have a real emotional need to be near them.
My parents forbid my brother or I to go into their room...and their were plenty of nights i really needed them, but was too scared to ask for their love. I learned to expect emotional distance from my parents...and i always feared asking them to help me with my emotional needs.
Perhaps a change of attitude is needed rather than a change of HIS behavior? i understand wanting your actual bed space back, and that is totally 100% your right! But why does he have to be alone? you and your husband get to sleep together and rely on each other for physical closeness, emotional bonding etc...why is your son relegated to "big enough to cope on his own" when he is still so in need of you both? Why does he have to be convinced that your agenda is what is best for him? Would your dh be on board for you convincing him that sleeping on the couch was better for 'both of you" (he'd think he was in trouble!)
I know i fought with one of my kids all night about this issue until i realized i was doing it b/c my mom, my grandma and my aunts warned me about how "he will never leave my bed!" I gave up fighting and filled his needs instead of society's, and within a few months he was happy to move into his big boy room all by himself after he knew he could trust me to really be there for him. Well, despite allowing that, i can assure you that my 19 yr old son does not sleep between me or my husband any longer ...but still feels safe and comfortable enough to join in the Sunday morning "snuggle" once in awhile!
Try reading Dr Sears...even though you don't want to start co-sleeping at this point, i think he makes a good argument for why little ones still need mom and dad long after our culture insists they are too big to deserve our tenderness! I promise that he will leave your room someday...and he will understand boundaries and not barging into your room...but 33 months is pretty early for him to be on board with all of our cultures rules!
Good luck, Momma!