Yes, that's exactly what I do. For me, this calculator was the most accurate: http://www.sophisticatedpair.com/bracalculator.htm. With an underbust measurement of 29", I usually end up in 30 bands. However, I can think of at least one brand where a 28 fits better and lasts longer because their bands are often stretchier than others.

It's possible that your issue is with both the cup and band sizing. You can isolate one from the other by putting the bra on backwards, with the cups in the back, and fastened on the last/loosest hooks. If you can pull the band more than 1/2" - 1" away from your body, the band size is probably too big. I say probably because some of this is personal preference. Yes, it looks a bit silly, but it rules out the possibility that any snugness you're feeling is from cups that are too small, rather than from a supportive, properly-sized band.