About the YSL Mombasa - It might not be perfect for you.
It is a gorgeous bag, and I adore mine. It is roomy, the shape is fabulous - I get compliments every single time I carry that bag - from the fashionista to the new-age artist who wouldn't know a designer if they walked up and introduced themselves.
BUT the handle is a royal pain. I might be the only one who feels that way - see Meg's review -
http://forum.purseblog.com/blog-entries/ysl-mombasa-83890.html
Mine is the 2007 pewter edition - I tried both the pewter and the horn, and it can dig painfully into the shoulder after a few hours. If I had it to do over again - I'd probably have considered the Vincennes a lot more (It has the same shape - but the handle is metal, without the digging into your shoulder pokey bits which bother me about the Mombasa)