You’re in luck!
Come on, there isn't even a button "install" on the sailfish website. You certainly have to go through the "developers" menu, but even there, it's not clear where to go to install it.
It does not fit att all the requirements
Such things sound cool but are untenable in the real world. Microsoft used to have downloadable binaries on websites (ActiveX) and that showed what a stupid idea it was :) There's a reason internet explorer has such a bad name.
It is arguably easier than installing windows on a laptop (if you were someone who had done neither before), since it is just a few buttons to press.
OP means it figuratively. Amazon's "one click" checkout isn't actually just one click, it's a metaphor for how simple they're going to make it for you to buy the item. Similarly, a "one click" install of another OS should be taken to mean "dead simple to install" instead. You're welcome to debate how easy it is to install Sailfish OS on those grounds, but if we're being pedantic then there's quite literally no solutions that actually fit the parent's description.