SUMMARY: Boost is fine probably.
The vet found nothing wrong with Boost even after doing a culture of her urine and testing for a few other things. So we're going back to the assumption that it's probably behavioral, because everything else that could be medical is both rare and harder to diagnose.
However, he did say that certain bacterial infections won't show up in the culture especially if they're mild, so let's try 10 days of antibiotics anyway and see whether it helps because sometimes it does. I'm leery of antibiotics just on general principles, but he felt from our long discussion that I had asked the right questions and tried the right things and said that, if it were his dog, he'd do it. So, OK, we're doing it.
I picked up the pills right before leaving town midday Friday and just got back. The dogsitter (Renter) said that she didn't wake him up at night and he saw no signs of puddles in the morning. Of course, I haven't even been up to my bedroom yet, so who knows--
But I'm back on thinking we'll simultaneously treat it as behavioral. Starting with, if she gets me up, she goes into her crate instead of on the bed when we come back in.