Tea tree’s is a pretty good anti-fungal, anti-bacterial anti-pretty much everything else. It’s usually not too strong for most people’s skin in short term use, but if you’re talking about douching, you’re talking about a mucosal membrane, not skin. Make sure it’s well diluted - 3 or 4 drops in a douche should do you.
I’m not a fan of douches at all, they’re too easy to abuse. I’d rather sit in a bath with some tea tree and lavender and perhaps chamomile (I make my baths stronger than **Zabali **- about 10 drops of each for a full bath if we’re doing a medicinal bath and not a spa treatment) and some infused calendula and crushed garlic (A handful of calendula and a few smashed cloves of garlic tied in some cheesecloth and put under the tap as the water fills). Smells nasty as all get out, but will kill anything that shouldn’t be growing on you. Put your essential oils in a Tablespoon of milk first - it emulsifies the e.o, so you don’t have an oil slick on the top of the bath.
The only other prevention tip I have is not to use powder of any kind on your girly bits. It gives the yeast food, and you’ll suddenly have bread dough, or something disgustingly like it.