At 3 weeks old I really wouldn't worry about creating bad habits.
Your son has had food, warmth and comfort (by hearing your heartbeat) for 9 months; he's trying to create that again by falling asleep on you- he feels safe enough to fall asleep on you 
So called 'friends' (or in my case family) will give you the spiel: "creating a rod for your own back feeding to sleep" etc but I just ignored them. It was my choice to breastfeed and by breastfeeding you are offering comfort and snuggles all at the same time.
What I will suggest, and it was only my experience with dd, is during her awake time, I'd put her in her Moses basket to catch up on things: legging it in/out of shower, tidying up after her, sorting washing etc. but she got used to it, used to look out and by about 4 weeks she used to drop off on her own. As the weeks went on she started to develop a habit of waking around 7.30am, feeding and then awake time for an hour, I'd hop in shower, be pottering and she'd go back to sleep on her own by 9.30. But I still feed to sleep at night now (she's 10 months) as its easy. But she will go off on her own too.
I'd love to say that was some magic parenting skill I had
who knows, she was fed on demand (or on cue, I'd catch her sleeping cues before crying) and never left her on her own to cry.
Just do what feels right for you. And congratulations too 