The easiest way is starting down at the ladder, so you are already into Discus i see. So you're already famiiar with low tech and how to run things and keep 'm in check. That still doesn't mean that you can skip the first half of the ladder and jump right to the top.
When you want to go high tech with co2 then you're far from easy if you do not have any experience nor understand the chemistry and physics basics involved. It ain't rocket seince but in way you need to know what you are doing. Then the easiest way to start is reading all tutorials regarding co2 all the basics you need to know are explained in there very adequate.
You could buy a nice starters kit
don't dive into deep or to expensive, look for example for a 2nd hand functional disposable botlle kit from somebody who decided to go a step further.
Then give it a try and keep the learned stuff from the tutorials in mind. Measure PH and KH add co2 see what you dropchecker does, measure again, see the table posted earlier in this topic and compare the results. Keep it green..
Add firts to make your plants grow. Mean while adding Co2 and other firts you probably will encounter other dificulties, like algae growth or plants getting into shortage of stuff, melting, coloring what ever, all kinds of things can happen.
Then you have UKAPS
ask questions about what you encounter and experience. People will help you to get a hang of it. After a while playing manualy and measuring this an that and so you'll find out soon enough if you like it enough to go a step further. By then you have learned the basics you need to know.
Then you can start spending big bucks for a nice automated system, with a timer switch and a co2 solenoid and maybe if you're rich enough a 150 buks PH controler.
Now what's easy about a PH smart controler.. Not so very much..
you still have to check your KH and PH and watch you fish and plants like a hawk every day and possibly reset your smart controller regularly. It aint smart all the way.. The controller will shut down the co2 when a certain PH value is reached. A value you have to set yourself regarding the measured KH value and desired co2 ppm and what you see in the plants and fish. If things are off you have to check again and find waths wrong, calibration of the controller, wrong KH test, to much or to less firts? The only easy thing is, you do not need to keep the bubble count manualy in check all the time.
So spending 150 buks for just that is depending on your salary maybe a bit to much. Even with a PH smart controler you need to set your bubble count in such a way that if the system fails and doesn't shut off you will never gass your fish or shrimps. They simply die of suffocation if you don't and if it fails when your not home or just not paying attention. Understand the dangers of the ease and then you'll see the PH smart controller isn't realy worth the money for the average hobbyist if you can't find a cheap used one. A good steady needle valve and a good fuctioning regulator is as sufficiant. With or without a smart controller you still need to pay attention anyway. Some people don't and gass their fish, i believe there are topics about that as well here at UKAPS only the real heros dare to post. I don't want to know the number of the silent non heros putting lots of lifes on the line but their own.
Smart?