You're overthinking it majorly.. If you are constantly thinking of body language techniques and trying to get 'perfect' body language, you will end up looking awkward AND will be concentrating on that so much that you won't speak as fluently and probably won't listen as well. Trust me on that one from experience..
Just relax, do whatever the hell you like. No matter how many tips you read of 'perfect relaxed state', the reality is if you
really are relaxed, it won't matter how you sit you will appear relaxed.
Be funny, be relaxed and confident, maybe practice facial expressions such as smiles in the mirror if you feel like it.. Girls comment on my sexy facial expressions, mostly smiles and the eyebrows raised thing. And have fun. There isn't really an easy way.. If there was, we wouldn't all be sitting around here.
Good luck.