From experience, don't relax it!
I went from very thick hair to very thin hair in one shot, it took years to recover. And it took years with me not relaxing it.
I think you could easily wear it wavy, you just have to do it right. The CG method is a good place to start, a lot of people gave good info on it.
If you REALLY want it straight, I'd invest in a good heat protectant first. Then a shower cap so you only have to do it once every few days.