I think that bras feel like torture devices, ugh! I take mine off immediately when I get home! Since you don't want to get a professional measurement taken, then the next best thing to do would be to try to find a bra that has no underwire in it (it also looks smoother under clothing but still offers support), and try on a lot of different sizes and brands until you find one that isn't to bad.

Also, try on the genie bra. It's kind of like a sports bra. It has light padding in it and it's made of cotton. There are other bras similar to it, but look for one to where there is no hole at the side as sometimes the padding can shift and end up being hard to smooth down or get even with the other side after washing it a few times.

Strapless bras with a wide middle might help too as I find that bra straps almost never stay in place with me. You can find some w/o the annoying under wire which is torture to wear and unnecessary for support IMHO.