I need to buy new tzitzit and I’m not sure whether I should buy with techelet, since its too expensive if its not neccessary. Also, what is the best material to buy.

Most of the Poskim Nowadays still wear Tzitzit without Techelet because of different Halachictic reasons, amongst them that we are not certain that the color we have is the real thing. Therefore it is possible to buy Tzitzit without Techelet. The best cloth for the garment of the Tzitzit and for the threads is sheep wool, with such you satisfy all the Poskim. Rabbi Ro'i Margalit