How do i keep my hair straight throughout the whole day?

okay so i don't straighten my hair EVERY day so dont spazz on me, but when i do, i tend to put it up sometimes.. and like 20 minutes later when i pull it out of the ponytail, theres a big dent it it. i know lots of people that like when they straighten their hair it stays straight even if thy put it in braidss and i really want my hair to be like that haha(: also, when i straighten my hair i make this little inwards flip at the bottom, and it tends to flip outwards or just go flat halfway through the day. So my question is: are there any products that could make my hair stay straight all day? or is it just the way my hair is that it molds into whatever shape it's put in? sorry that im rambling hahaa.. but ALSOOO please dont say hairspray because it always makes my hair sticky and un-soft. Thanks so much and sorry that this is so longg... hehe(: