HI there. To clarify my previous post - I have found Wacoal underwear (panties, more expensive) with no seams at all, and a flat waistband. They are very stretchy. I also wear Jockey cotton briefs (less expensive, but not cheap) inside out so the side seams don't rub. I don't know why the waist doesn't bother me, but it's okay. Also, if you can find a good quality poly or blend cami, rather than very high-priced silk, go for it!
I'm very lucky not to have to wear a bra (double mastectomy). I'm grateful I don't have to find one that would work for me, but sorry I can't make any recommendations about that. Good luck to you all.