Are you saying that you don’t want to begin your transition until sometime net yr? (after your senior yr of hs?) If so, then this would mean that you will continue to get relaxers up until that time. If you actually plan to stop getting relaxers now, you will be beginning your transition immediately. Transitioning begins when you stop relaxing your hair, regardless of how you style or maintain it. The transition will be intimate regardless of what you do because only you can determine when, if, and how long it will last. Only you can place a significance value on it that in itself, makes it an intimate experience.
You can still straighten your hair when transitioning and even once you are completely natural. There are some naturals who only where their hair straight, and that is ok if that is what they want to do. It sounds like you want to continue to wear straight hair, but without chemicals. I would suggest you begin by taking good care of my hair (moisturizing, deep treatments etc) and definitely use heat protectants for straightening. Then trim as you go along until all the permed ends are gone. I personally would not want to do this only because of my FEAR of damage/breakage. However, I have a BFF who only wears her hair flat ironed and has done so for years. Her hair is long, thick, and appears to be healthy. HTH, Good luck