need help with hair

Hi, I'm a guy with very curly thick long hair. I mean, if I get it wet and let it dry, it actually curls upwards--corkscrew like. I have been using a flat iron for the past couple months and it has been great. Tho, on 1st day hair it makes it too straight and I look like a lumberjack minus the beard and moustache...so sometimes I put a small amount of mousse or water in my hair to make it curl a little.
My question is...is there any type of oil I can put in my hair that will give the effect of natural oil (2-3 day hair) WITHOUT it curling it all the way back up again? Also, does mousse make hair any drier at all? It is winter where I live, so my hair tends to stay pretty straight after I've flatironed it. But in the warmer weather, it doesn't take long to get the look I want since it curls up faster...but not all the way thank goodness.