Yeah... I think you have it right. Well, almost! I believe that ring slings are newer; they are basically rebozos that use metal rings instead of a knot.

I have certainly used both, but I favor ring slings...it's definitely a personal choice...totally up to whatever works best for you. If you want, buy/find a piece of fabric and try it out as a rebozo, and if you don't like it, turn it into a RS!
If you're looking for wraps to use as rebozos, the keywords you need are "shorty" and "rebozo." They'll be somewhere around 2.5 meters long and usually around 25 inches wide. I wouldn't worry about the brand of your wrap... it can be intimidating to make a selection from so many different kinds of woven fabrics, fiber contents, and designs. Just pick something you like the look of, and once you get to working with it, you'll know your personal preferences better and can make a better choice the second time (and often you can trade or sell for funds for your next wrap!)
RS brands... also lots. Just to keep it short, I'd recommend Sleeping Baby or Comfy Joey. Lots of people like their shoulder styles (how the fabric is arranged before it is sewn around the rings), but there are many, many more out there that have strong fan bases too (Psling, Maya LP, Kalea, etc).
Either way, both are highly usable for both a 7 mo and a newborn.
Links... maybe there are some in the stickies at the top of this forum? Also, you can visit thebabywearer.com for articles and a very supportive forum, much like the one here.