A bit of an improvement: do `space, V, enter` instead of `0, space, $, enter`. A single <kbd>V</kbd> is a lot easier to type than a <kbd>0</kbd> and a <kbd>$</kbd>. <kbd>V</kbd> is equivalent to vim's "do visual mode select of entire line" command.

I can't speak to byobu directly but since it's just fronting tmux, you could also bind a key to all this in native tmux. Something like this:

 bind-key -r -T copy-mode-vi Y send-keys -X begin-selection \; send-keys -X select-line \; send-keys -X copy-selection

Then you just enter copy mode, go to the line you want to copy, press <kbd>Y</kbd> then <kbd>Enter</kbd>. The line will now be in the paste buffer. (While that's a bit long and ugly it does work for me.)

**Edit:** Tested with tmux 2.4