I've just had a quick look, and there are some very small BGA-packaged STM32 chips about. With a competent PCB fab you might be able to knock together a board with 8 jumper pins that wouldn't be much bigger in total than a SOIP attiny, but that's another job plus whatever peripheral components need to be added. Might be a fun design job, though.

https://www.mouser.co.uk/ProductDetail/STMicroelectronics/ST... looks like it might be a lot of fun, but it's got a 6 month lead time on it.