Hmmmmm. Everyone I know who knits IRL seems to say "I knit tight" - myself included. However the sweater I am making for my son in a size 6 - he will be 4 but he's tall and I want this to fit a while - is so far looking ginormous and I fear he will be wearing it until he is 12. So maybe you do loosen up with time and I just think of myself as a tight knitter because I used to be.
At any rate, I know for a fact I cast on too tight and I think that once you start tight it is hard to loosen up - it's like you think well if I make the next row loose it will look dumb. So because of this and because I don't want an edge that won't stretch enough, I usually cast on with a needle 1-2 sizes larger than the needle I will be using to knit. I find a loose cast-on row puts me in a loose state of mind.
Sorry if this has been said - I didn't see it said but I may have missed it.
And I agree don't use cotton now! Cotton is easier to crochet with than to knit, IMO. I can crochet with cotton but knitting with it, I always end up with stubborn tight stitches that won't move.
I don't know about the bamboo... I think most people find yarn to not slide as well on wood so it could be a problem. Personally I will only use metal needles.
Oh - and don't knit when you are hot! If it is hot sit near a fan - I find the sweatier my hands the tighter my stitches get.
Summary - give yourself time, cast on big, don't use cotton, stay cool and dry.
Oh - and have fun. Don't forget to have fun.