Lately we've been finding that we can only keep quality bakery bread loaves on the counter for about 5 days before they start to mold. We'd like to get a little longer out of them -- say 8-9 days -- because while stale at 1 week, they're still good for toast and croutons if not moldy.
We buy unsliced artisan bakery loves, sometimes from the bakery directly sometimes from grocery stores that get daily delivery. These are large French or sourdough loaves (1lbs to 2lbs), or 1.5lbs whole wheat sandwich loaves. They are generally preservative-free.
We store them on the counter, in a heavy paper bag during humid weather or in a thin plastic bag (like a produce bag) during drier weather (we don't reuse bags between loaves). They are in a shaded spot on the counter. We live in the US Pacific Northwest and do not have air conditioning, so ambient conditions are generally between 40%-70% relative humidity and 60F (15C) to 80F (25C) inside the house, depending on the season. The time-to-mold doesn't seem to vary much with the season, though.
I'd already tried cleaning our counters extensively using soap and vinegar and some moldkiller, and that didn't seem to change anything.
So, question: What else can I do to extend the loaves' time on the counter by a few more days before they go moldy? I am asking for practical tips that you have actually tried, or have citations for real-world testing.
Notes: not looking for advice that involves freezing or preservatives or changing bread brands. I read this question, but it's about changing the bread recipe, not about techniques to preserve a bought loaf. I saw the UV idea, but haven't been able to find anyone who has personal experience with using one and obviously it's quite a project. I've also looked at most of the advice in articles like this, but they don't give sources for their advice or any evidence that they've tested it, and some of it is contradictory.