You will find that many of us on here love kwigy bo alex carriers. But, the only problem is that if there is a question as to if your baby will be more or less than 5-6 pounds full grown, you may want the larger size~just in case.
Other than that. My number one suggestion~ make sure it is fully enclosed (it can zip up all the way so that that cute little head, or more, won't pop out of the bag)!
There are many great carriers out there (and I have had most). I'm obsessed with carriers and so is my little one. It is the one thing she LOVES (she's not a fan of toys) so that is what she gets for birthdays, christmas, or just because.
I do have a few of my carriers that I am selling so that I can make room for more
I have one that I loved when my little girl was a puppy because it had a zipper expansion to make it bigger as the dog grew.
If you want info on the ones that I have, just let me know and I'll send you an email with pics and info on each one.