I've found it more reliable to use a tape measure (the soft flexible kind, like for sewing) around the hips than the waist. Ultimately, whichever measurement is bigger, go from there, and go a size up if you're still on the verge.
Picking a larger size will mean a higher rise and more overlap in the taping... But in my experience, too small means you struggle to make the tape even reach, and that will cause uncomfortable constriction around your legs (and more frequent tape failures!)
Bambinos run a good half size small. I'm right in the middle of the range of the larges with a 38" beltline. The mediums should work well for you, though you are probably toward the low end of their coverage.
I have a 26" waist. Usually, I have to pull Bambino tapes pretty close to my center to get it snug, but it works and I don't have any issues with it falling off or anything (which is what I'm imagining what you're thinking because I used to think the same thing). Usually, mine rides up to my belly button. When I first tried it, it felt really thick (which I personally really like ), and that's mostly because of the diaper itself, and not the sizing.