Aww "bad habits" sounds so strict when they're so little, 2 weeks seems so soon after being inside you for 9 months, no wonder he still loves being close and probably reacts very quickly and noisily to being set down or left.
The sling is a good idea, do what you can wearing it and carrying him next to you. Can I ask do you have a moses basket or cot, I would try first of all sleeping with a t-shirt of mine under me for a couple of nights then when you put him down to snooze, let him lie on that in his moses basket or cot so he can smell his Mum. Or just use the same comfort blanket, (better have two so one is in the wash while the other's in use). Even better have a hot water bottle in there beforehand, (obviously remove it before laying him down), that way he is cosy and not lying on a cool sheet.
People have recommended white noise, that is supposed to be soothing for daytime naps. Doesn't work for everyone.
At night time I would give swaddling a go, sounds biblical but it can feel reassuring to little ones.
I don't what you found worked with your 3 year old at this stage, in all honesty I don't think I found a reliable method until mine were both at least 3 months or so. A friend of mine had her mother come and stay, was thrilled Gran had no problem rocking baby to sleep. When she returned home, my friend found her DD wouldn't settle without up to an hour's walking or rocking.