When I was buying pinks from the Petco here, their pinks were usually quite small, but their fuzzies, the next size up, were very big. I ended up feeding two pinks for quite awhile, until Tavi was big enough to take a Petco fuzzy.
Most people will double up their mice, if they've still got some leftover that the snake has outgrown. I think the main reason you want to go up in the size of the mouse, rather than just doubling up, is the older the mouse, generally the more nutrition it has, especially calcium. That's more true when the snake is on pinks than older mice. So while you'd want them to advance in size for that reason, if you think they'd be less likely to regurge two smaller mice than the next size up you can find, doubling is best. It won't hurt for them to be on doubles for a bit when your finishing off that size of mouse, either.