OMG I cannot recommend these enough. Fabulous at all ages.
A newborn in them is great as they are positioned like in the womb and can sleep well snuggled into you as they're comforted by your heartbeat and smell.
When my DS was around 5 months old I either had him facing me if he was a little sleepy (that way if he drifted off I could put some material around the back of his head to stop him lolling). If he was wide awake or when he was a bit older I had him facing forwards, he loved being close to me and being able to see the world around him.
My DH and I never had any problems with it feeling too stretchy and found it great for me to carry DS even with a bad back and recovering from SPD during pregnancy.
My DH loved carrying DS in it so I would recommend a neutral colour like navy so that men can use it too. Another positive is that you can bf discreetly if you wanted.
One downside is that they can get a little too hot in warm weather. When I went to Spain when DS was 5 months I used the Kari-Me most of the time but had a cotton material one for during the day. I much preferred the Kari-Me as I could take DS in and out for nappy changes etc and leave the wrap on. As the other one was cotton weave and not stretchy I had to take the whole thing on and off.
Expect to get lots of lovely comments. People were always telling me that DS looked more comfortable than babies in baby carriers (I felt more comfortable too as DS was happy and his weight was well distributed).
The Kari-Me's can actually be used as hip and back carriers for children upto 15kgs or 3 years so def ok for your little one. I hope you get one and love it as much as I did.
Don't bother buying a used one from eBay as they hold their value well and are not much cheaper than new. Mine cost £32.95 last year inc p&p but I can't remember which site I got it from.