Two spaces after a period was taught in a lot of prep schools for years. I personally still prefer it since it allows my eye to rest a moment longer as my brain processes the fact that a new thought is coming next.
But that is just me and I am well aware that the single space after a period has been pushed a long time as the proper construction.
Two spaces was never correct typesetting. Never. However, like most things, necessity (manual typewriters and non-uniform typeset sizing) led people to start doing it. However, you can pick any professional publication anywhere in the world, any year of the world, and you would find that 1 space after a period has always been the convention.
Most publications are fully justified, so the spacing between words is almost alway irregular. Your comment about a place to rest your eyes doesn’t make much sense to me.
You’ll notice, even on your phone, when you hit two spaces at the end of a sentence it will add the period and a single space. Two spaces has become an accepted norm by most style manuals, but all I’ve ever looked at state a single space is the proper convention.
I find people who use 2 spaces are 45 or older and all claim it’s too difficult to change or looks weird. I, too, learned with two spaces after a period; it took me 1 long report to break myself of the habit. To me, it looks clunky, especially with full justification, but to each his/her/their/tree/sponge own.