work with RS232 protocol, therefore you must convert them to TTL protocol
Yes except you are using the wrong word, what you mean is “hardware standard” not “protocol “. A protocol is system of actions or messages used to communicate and is defined in your software alone.
I know that my soldering skill is ridiculous
It looks like it is your iron not you that is ridiculous not you. It is not getting hot enough to make a proper joint.
2- please, inform me if my solution works
Well I think you have to inform us if it works, but if you have RS232 signal levels you do have to convert them to TTL levels.