Lineage OS

As far as I understood, I should look for unofficial OS from developers of LOS. I am not storing any important data on my device but, you know there is some accounts credentials and private chats.

This would add at least a bit credibility to the ROM, but in the end you don't know what's inside. The device maintainer can implement anything into the source code they would want to. Is that a realistic scenario? Probably not, but it should be considered before flashing stuff from unknown sources.

do you recommend to use LOS for me
It depends.

Tbh, only if you really want it. From the info you provided I get that you are mainly interested in privacy.

In case you would flash an unofficial ROM that works without bugs, you would need to avoid GApps, which is required to use the Google Play Services (Maps, Network Location, Push Notifications. This is the core of Googles surveillance framework.
Also keep in mind the monthly security patches are not guaranteed with an unofficial ROM.

If I were you I would try to live with what you have now. If you can, save some money and buy a device that is officially supported by LOS (meaning it is listed here).
If you can afford it and can live with a more minimal system, buy a used Pixel and flash GrapheneOS for maximum privacy/security.

You are welcome to ask some more questions if you like and I will try to answer them tomorrow, but I had a lot of red wine and it is late in my time zone ;)