At least in American English “next to best” would mean second whereas “next best thing” means something likely to be the best thing in the near future and it’s a very common idiom.

i am american and think "next best thing" means second best. maybe "next big thing" would be better but is a bit generic

To jump in on the confusion, I'm American and have seen it used both ways, completely dependent on context. When I read the original comment I understood it as 'next thing that we all think is best' rather than 'second best.'

But after reading the comments and thinking on it, I realize it's probably used more often in the context of 'second best.'

I think you might be referring to the common american english idiom "next big thing", as "next best thing" means 2nd best in american english as well.

Note that "next bigGEST thing" also means the 2nd biggest thing.

Do you not have sentence structures along the line of "I wanted the premium model but it was out of my budget so I went for the next best thing"?

I get we're trying to go for "next [best thing]" but yeah I (also UK) read it as "[next best] thing" and can't think of any examples where I'd read it as the former