gelled toner, like this one, and adding tea tree oil with the solubilizer (like the Caprol Micro Express I used in it). Or consider making an oil free moisturizer, like this one. Just add your tea tree oil at 1% to 5% (although that's quite high, in my humble opinion) in the cool down phase. Remove the same percentage from your water phase.
Here's a post I wrote recently on facial moisturizers with tons of links!
Join me tomorrow as we take a look at the chemistry of essential oils!