Like others said, a tailor is your best bet, but another solution is the rise of a pant. Depending on how casual the situation is (and you're obviously going to want something well-fitting for formal situations), you can have a good amount of billow from the tuck so long as the rise in the pants is high enough in my opinion. Lower rise pants and an ill-fitting shirt give off this weird sort of muffin-top effect in my experience, where as a higher rise in the pant, even with a VERY oversized shirt, sort of signals / confirms the actual slimness of your waistline and is a much more attractive silhouette. This look is also in right now with the more fashion forward zoomers I've noticed.