Wanting to know about types of hair extentions?

Myself and myfriend were discussing about hair extentions and they different types.....we are both used to wearing clip in extentions but want a nice head of hair!
we are both afraid of getting the platted extentions where they plat your hair and sow the hair into plat's! i bleach my hair and my friend has fine hair and is afraid its going to really damage our own hair from the plats!
we dont want to go down the route of the glue extentions either! what else is out there and whats best?
does the platted extentions ruin your orginal hair?
and how much does it usually cost?