D.,
people have mentioned ring slings (the Maya wrap is a sling, FYI), pouches, and buckle carriers (Bjorn and Ergo). These are all good options. Both slings and pouches are "one-shoulder" carriers, so if your baby is heavy, or you have back trouble, IMO these are not the best carriers for walking around the City (but good for quick trips to the store). Once your baby is about six months old, he/she really is too big for a pouch, though a sling will work up through toddler-hood.
You are right, the Bjorn is not a good carrier for babies' spinal development. When a child is in a carrier, the knees need to be higher than the bum (imagine a kid squatting), and the back should be able to be in the natural curved position, which the Bjorn does not promote (also, the Bjorn isn't recommended after the first six months). The Ergo is a good carrier, but not the only other option out there - I like the Beco more, b'c of the wider range of color/design options, but mostly, I find it fits my body-type better.
Since you are in NYC, why don't you check out the carriers sold at Metro Minis, 821 Park Avenue (corner of 75th Street, ###-###-#### (www.metrominis.com). The manager, Bianca, is a friend of mine, and is extremely knowledgeable. She can help you find a carrier that fits your life-style, body-shape and taste; they have a huge selection of a variety of carriers. There is also a "babywearing" parenting group (it meets at the store the second Saturday of the month from 3-5pm) where parents bring their carriers and kids and share tips, ask for help, and check out different carriers in real life. If you want more info on the group, check out www.slingsinthecity.com.
I hope this helps some! Here in Jersey City, I help organize the babywearing meetings for our area, so feel free to contact me anytime for more info. I wanted to give you more information in this response, but this has actually taken me over an hour to write, b'c I'm also taking care of my toddler! :lol: