How to mark text messages?

Hi,

I'm trying out a friend's iphone 6 plus because I'm curious if it's better than staying with Android on Samsung.

I would switch but there is just one problem--- is there no way to mark text messages?? Any app that let's me mark them unread or just plain mark them as important??

I go through so many text messages and I don't reply to them all right away, I need time to respond to many and I would hate to lose track of them on my iphone.

On my android I can just easily start to type into them, then leave, any they will be marked as "draft"

On ios if I do that, I have to remember to go back to it otherwise it gets forgotten, argh so frustrating apple, such a simple feature!!