I need hair tips. Details inside...

I have long, thick hair and to flat iron it myself, we’re talking an hour…

What I would love to be able to do is flat iron it, have it stay in for 3 days, then be able to wash it. It can easily stay in for three days and look lovely. I’m wondering if there is a particular type of shampoo (or tips) that I could use, so, that my hair would stay relatively clean for those three days. Unfortunately, I have to use a bit of product in my hair before styling..