Dont try to elevate your free testosterone levels solely through testosterone boosters. You will fail. Your sport nutrition shop won’t :)
Almost no substance - including most known ones such as tribulus or erycome logifolia - has the notable ability to raise free T level. There has been minimal success with D-aspartic acid, phytosterols and boron citrate if combined with intensive workouts, but that has almost zero effect on your physiology.
But we have good news. There are some approaches which offers moderate improvement in your general health (following by elevated free testosterone):
a) Enjoy food and nootrients that consist hormones in traces, such as royal jelly or pine pollen. Avoid prohormones and steroids.
b) Enjoy food that decrease estrogen production in males - white button mushroom are tasty and excellent antiaromatic shrooms which block transformation of testosterone to estradiol. I recomend the same if you are a woman.
c) Avoid mixed estrogen agonist/antagonist such as soy. Pay attention also if you are consuming a lot of green tea since turn off your testosteron binding sites (SHBG or SSBG).
d) enjoy lot of hi-quality adaptogens such as Panax ginseng, Rhodiola rosea, Ashwagandha, Cordyceps in fermented mode - the most successful tactics is to lower your stress hormone cortisol (since both testosterone and cortisole are produced from the same precursor and they compete with each other)
e) exercise intensively, but not over 75 minutes (combine HIIT, complex free-weights exercises, intervals cardio - avoid chronic cardio)
f) enjoy hi-protein meals with lots of fat. Avoid insuline spiking simple sugars, but don’t go near paleo or keto (it will kill your T even more than McDonalds).
h) Avoid stress or let’s put it better, try to manage it.
Oh, and make love. Really. Its super efficient biofeedback.