Can't believe nobody replied yet! I had a clingy one too who also is a light sleeper. I persevered getting her used to lying down next to me and being cuddled on the bed, then I could roll away but be ready with a hand on her if she noticed. Then at some point I guess I started putting her down but I can't honestly remember when - I do know at 7 months I was mostly cuddling her then putting her down when just asleep. I think keep in mind what you are aiming for and just make baby steps towards it.
Not sure about waking up if you move away at night though as never coslept in earnest. He's still very small though, it will work out soon enough :-)
After all the sleep books I read for DS1, I should know the answer to this, but I can't remember.
DS2 is 4 months and has all his naps and evening sleep in the sling. If I put him down he usually wakes up within 5 minutes. On the rare occasions he has stayed asleep for a whole sleep cycle after I've put him down asleep in the evening, he wakes at the end of the first sleep cycle and will then be awake for another 1.5 hours before getting tired again, irrespective of whether I rock/bf/whatever.
He is a light sleeper in that he usually needs rocking/bouncing between sleep cycles or he wakes up. In the day he will often wake if I sit/kneel down, or if I go into somewhere with a very different temperature, or if DS1 is tantrumming loudly.
We co-sleep at night and he sleeps really well as long as I'm next to him. If I get out of bed, he often wakes within the next 5 minutes.
He feeds back to sleep lying on his side at night. If I roll him onto his back he wakes right up and I have to start the whole process again. So he generally goes to sleep sort of on his side and gradually moves onto his back eventually (I usually start feeding then fall asleep again myself).
He doesn't have reflux AFAIK and is perfectly happy on his back in the day.
I don't mind him being in the sling most of the time, but it would be lovely for DH and me to be able to have a proper cuddle without a baby strapped to me.