If in doubt, use two spaces.
Any 'nerdy' typesetter who insists you are wrong can always do a 'search & replace', replacing all double spaces with single spaces.
Of course, they may need to repeat the action in case you've accidentally typed a triple space.

Alternately (if it makes you feel happier) use only single spaces. If that goes against their 'style guide' they can do a search & replace for any full stop (period) which is followed by a space.

In these days of word-processing the argument is somewhat pointless