I can't win either. I get a bigger size to fit my butt but then it's baggy around my legs and too loose around my waist so I need to wear belts for high waisted jeans. I get a smaller size and it's too tight in some places or everywhere. It's what you get for being curvy. I'd recommend getting stretchy jeans so they can stretch around your curvy bits. I usually wear leggings nowadays, they're the only things that fit and feel comfy. Plus, they're hotter when you have a big bum ;D
lol... i don't think any woman on the planet can easily find jeans that fit... i know i can't :)
jeans are pretty easy to alter though... i'd just get a different brand and have a tailor take in the parts that are too loose... waist alterations are fairly common, inexpensive, and they do them all the the time so it's not really anything to be embarrassed about.
there's a ton of places that make shaping underwear... i know know Jockey does. Usually it's for the waist but they make a lot to compress the hips too.
if you can't get them altered, the belt idea is a good temporary thing... but trust me, you don't wanna start relying on them... i went down that path, now i have wear them everyday :( ... it really cuts down on my coordinating options!
i've gotten a few pairs from makeyourownjeans. com... for a few bucks they put in elastic in the waistband... you never have worry about a loose waist again :)
also Hollywood Fashion Secrets sells a special belt, 'Hip Hugger' that only goes in the back half of the waist, so it's not bulky or noticable in the front... i haven't tried it yet but it seems cool and i probably will