Yes, this is one of those situations in which you just have to make a choice and stick with it--do be consistent. And if you do choose to add the apostrophe before the -s, you still have to include the contraction apostrophe in don't's (just as I've written it).

If you're asking because of a work issue, be aware that many companies that deal in writing have official style manuals, where these questions might be answered. Or then again, they might not.

This question reminds me of a child's TV show I used to watch when I was pre-kindergarten age, where the teacher/hostess did a little skit with bumblebee puppets. It was called "Do Be a Do-Bee, Don't Be a Don't-Bee." Funny what our brains file away for future reference, isn't it?