For postflop, instead of studying a lot of game theory or getting software with a difficult learning curve like Pio, you might begin by just giving a lot of thought to your own range. In spots where you bluff the river, for example, what other combos in your range are your bluffing? Do you have much of a value betting range? The key idea is that any time you have a betting range, you want both value and bluff hands in it ... and the smaller your sizing, the more weighted toward value hands. 

So it can be very helpful to start off just by looking at hands you play and thinking about what your full value and bluff ranges are before getting too deep into the math of it. 

Riceman also has some great suggestions. A good understanding of GTO play is necessary in order to figure out how far away from it you can deviate in order to exploit the many weaknesses your opponents will usually have.

Slightly disappointed that I need to emerge from forum semi-retirement here to help you...I'm surprised nobody has answered you. You see? Without the Riceman the forums disintegrate. I really feel I should be on a retainer over here (joke)...I have been super busy recently is all, TPE still owns my soul. 

Where to start? Well, I have been almost clueless myself regarding GTO rather publicly in this very forum, checking out some of the threads here at TPE in this forum might be a good place to start. Apparently Ed Miller's Poker's 1% is a great introduction to GTO. Not read it myself. Would stay away from Tipton's Expert HUNLHE, or Chen/Ankenman's The Mathematics of Poker until you have grasped the basics. Start out with Ed Miller. 

Software...well you are on the right lines for pre-flop GTO calculators with ICMizer. Personally I use HoldemResources for ICM calculations, and SnapShove for chipEV. Post flop I understand CREV can approximate GTO lines...not sure about this though, and I am unfamiliar with the tool. Unfamiliar also with GTO Range Builder.

PokerSnowie I have had from day one. I love Snowie, and it has the great feature that you can play vs. the bot, and it gives you feedback on your play. Apparently I am "World Class". Right. I wish someone would tell that to the RNG at Pokerstars. Nevertheless, my game has improved enormously playing vs. Snowie, no question, and I use the engine to warm up HU before a session. The marketing was all around GTO when it came out, but they had to swallow some humble pie under a barrage of wrath from some GTO experts on 2+2. I'll stick up for Snowie all the way. I have no idea if it plays GTO or not, but it sure beats me long term, so I must have something to learn from it.

Andrew Brokos and Matt (Ginger45) are the resident GTO experts here at TPE. They are great minds, and they give of themselves freely in these forums. Andrew's Range Construction series revolves around GTO concepts, but it is quite a challenging listen/ watch/ whatever. Perhaps not ideal to grasp the basics.

Hey! Hope that helped...

So I have decided to start taking a heavy focus on the mathematics of poker and a more "GTO" approach to the game and wondering where to start in regards to what books I should be checking out and also what programs I should buy to use for hand analysis? And pretty much anything that will help me understand and implement a more GTO approach to my thought processes in game. I have dabbled in looking through Nash calculators and ICMizer (Free Version) but really want to grow a deep understanding in this area.

I am incredibly shit when it comes to maths so all the help I can get would be amazing

<3