I have the same problem--my hips are a 5 but my waist is a 3, so most jeans I try on have that unattractive gap in the back. It's so annoying. What I've found that really helps is getting the stretchy jeans; I know a lot of people don't like them, but I haven't had as big a problem with the gap thing (plus, you can get them to really fit your butt
and still be able to sit down comfortably
). Most of mine are XOXO--just because I used to work retail and I could get them really cheeeap--but I'm getting ready to get a new pair or two, so if I find some that fit nicely I'll let you know!