jasda3350,
I'm not going to tell you what to rush out and buy because both methods, mixer and "tank" steering, will work BUT both make different demands on your skills. I'm happy to sail with either method, provided the model is moving at modest speeds. Steering a fast model with differential control of the throttles can, in my experience, be a very imprecise method.
Also, does your transmitter have any built in mixing functions? What you want is often termed ELEVON-MIX and will combine the conventional rudder+throttle sticks in the fashion you want.
So, I suggest that you buy a second ESC, which you are going to need with either method of controlling the model, and try "tank steering first. If you like it, a tip is to imagine you are holding the model in your hands when operating the transmitter so your fingers on the sticks are trying to rotate the model, that's great. If the transmitter does not have a built in mixer then at least you will be deciding if you want to buy a separate item to install in your model.
Let us know how you go on.
GlynnG