if you are in Y then finnair have economy comfort which is the same seat but about 10cm extra legroom. you have to pay for them (previously they were free for sapphire card holders).
I have never really seen a "reasonably" priced airport upgrade to business. With BA they would offer premium economy but the upgrade at check in isn't offered for those on connecting flights (i never get the option to buy one for any HEL-LHR-XXX trip. Only direct flights from LHR).