I find mei tais very easy to use. The kind I use is here
http://www.kozycarrier.homestead.com/Kozyinfo.html
If you want to use it "in and out" you can fold it down around your waist and tie it until you want to put DD in again. I do this when shopping quite often. Since it is a two shoulder carrier that you also tie around your waist, it is much easier on your back. You can use a mei tai until 35lbs or when ever you decide to stop wearing your baby.

I can easily wear my DS (about 40lbs) or DD (about 50 lbs) in it and it doesn't bug my back.

A wrap is another good idea. It takes longer to learn, but within a week I had a couple different carries figured out. The "forward cross carry" (or FCC) is "poppable". You can tie it on and get baby in and out without taking the wrap off. This site has many types of wraps.
http://store.attachedtobaby.com/sear...x?categoryid=4
The wrap I have is a SPOC (Simple Piece Of Cloth) made from some gauze I bought at Wal-Mart. Very nice for summer.
I can answer any more questions you have (or at least try!), just let me know.