FTR: I'm a lawyer and was taught to use two spaces from elementary school on. I tried to get my firm to change over to one space about six years ago.
I lost that battle to the old crew who thought it helped readability. Just like double spacing.
There is a more excellent way. Just read some US Supreme Court slip opinions and you'll see how great typography can help readability.
Hint: SCOTUS doesn't use two spaces or double spacing.