Honestly? I really liked dextromethorphan. Read up on it. High ld50 compared to psychoactive levels, neuroprotective effects, synergistic with a lot of other drugs, legal, easy to acquire (get the orange label robitussin in the US. easy to find during cold/flu season. the shit that contains guafenisin is also doable, but guafenisin makes you sleepy and you'll pee sand.
DXM is very synergistic with diphenhydramine (common benadryl for name brand), they both use the same enzyme in the liver to metabolize, and dph is an anti-emetic which is helpful when you're taking dxm hydrobromide. you'll be nauseus, and you'll want to drink a metric fuckton of water if you chug a bottle of syrup (gelcaps are better, but the coating on them is hellish. you can slit the caps, drain the fluid, or slit and swallow to decrease onset time).
you can do a simple acid/base extraction to create dxm citrate, which is a hellish lemon concentrate instead that you could either dilute into a jug of trippin lemonade (label if you make this and keep it in the fridge, i never had the courage), or take as a motherfucker shot (find something to cover it with. i never did, but i have faith that you're smarter than i am). irregardless, you're putting something very acidic on your teeth, so rinse with a neutralizer like a baking soda solution afterwards if you like your tooth enamel. (since i have no face to lose for an Unpopular belief: stop using flouride, it breaks down repair enzymes in your mouth that help fix enamel to a degree)
if you're not comfortable doing that extraction, don't do it. that said, if you're a overcautious at every step and use actual equipment, it shouldn't go to bad. chemfags can chime in at this point.
i'm not going to cite shit, because you've either got the common sense to use this as a jumping point to start digging around and figuring shit out or you're a dumbass who's going to go take pharmaceutical compounds on the advice of an internet stranger.
good luck friend, and feel free to ask any questions.