Any supplements that lower sex hormone binding globulin should raise free testosterone through a feedback loop. So technically you can just search for ideas by looking up things that lower shbg. Ppl forget that sink, magnesium, D3 and a few other vitamins/minerals will help, myself included. I often overlook those. DHEA and Pregnenolone are precursors/prohormones to other hormones and those can help as well. Just remember with DHEA that you can't really control what other hormones it converts to so you may very well get a spike in estrogen along with it.
Also, exemestane lowers estrogen and raises free testosterone, so in a event that something your doing raises estrogen, a lil exem would help with both. I'm not saying to go take a AI for no reason tho