So am I right in thinking that sequences built via yielding are necessarily unbuffered, and that if I want some buffering I'll need to use channels?

What do you mean "buffered"? If just collect each N values to list it's possible using chunked operator But you just should understand that sequences are sequential, they are not asyncronous, they block consumer, so

buffer

in this case doesn't make a lot of sense, producer and consumer block each other nothing to buffer in terms of asyncronous work